Xu Shaofeng investigated the influence of temperature and pressure change on the accuracy of HLS testing and proposed a temperature correction model considering the pipe’s expansion coefficient. Chen Jihua thought that the uneven temperature would lead to uneven liquid density in the HLS, which leads to the test error he also proposed a preliminary approach to eliminate temperature impact. In actual engineering, the temperature change is considered the most important influencing factor during settlement detection. The influence of pressure difference can be eliminated using equal-pressure pipes. Among them, the earth tides and gravity anomaly can only be filtered under constant temperature, and their influence can be ignored for nonprecision engineering because of the micron-level effect. However, the accuracy of the HLS is disturbed by factors, including temperature changes, pressure differences, earth tides, and gravity anomalies. The basic principle of the hydrostatic levelling system (HLS) is the liquid connector, which means that, by measuring the relative change of the liquid level in the levelling bowl at different positions, the settlement or uplift of each monitoring point relative to the base point can be determined. Because of the simple structure, high accuracy, strong stability, and little influence from the external environment, hydrostatic levelling is widely used in the subsidence monitorization of major projects such as subways, bridges, tunnels, dams, and nuclear power plants. Although the CCD optical imaging sensors, laser convergence sensors, and fibre grating sensors have the advantages of high accuracy, strong modality to the terrain, and a high degree of automation, the construction and maintenance costs are relatively high, and their anti-interference performance is poor. The accuracy of GPS measurement for plane relative positioning has reached 0.1–1 × 10 −6, but its elevation measurement accuracy is only 10 −2, which cannot meet some projects’ accuracy requirements, and GPS is expensive. Among them, geometric levelling and trigonometric levelling are costly and inaccurate besides, they are limited by topographical fluctuations and challenging to realize real-time monitoring. Settlement monitoring methods include geometric levelling, trigonometric levelling, GPS measurement, CCD optical imaging measurement, laser convergence measurement, hydrostatic levelling, and fibre grating measurement. Therefore, the accurate measurement for the settlement or deformation is crucial and can provide a scientific reference for the design, construction, and operation of major foundation projects moreover, reliable data for numerical engineering analysis and long-term deformation prediction can be provided. With the rapid socioeconomic development and urbanization, major national infrastructure projects, such as high-speed railways, large-span bridges, ultralong tunnels, high-rise buildings, integrated pipeline corridors, and dams, are increasing their uneven settlement, deformation, and foundations are a precursor to the engineering failure. The relative temperature influence coefficient increases as distance measurement increases, and the HLS test error caused by T A will maintain a constant value when the distance measurement exceeds a certain value. The temperature influence coefficient of a single HSL case is linearly related to the expansion coefficient deviation between the refrigerant and pipe the test error of the double HLS case caused by T A is attributed to the expansion coefficient deviation of the pipe and the refrigerant between the base station and the measuring point. The test results show that the elevation of a single HSL case has a linear correlation with the ambient temperature when the temperature rise rate is greater than 0.1☌/min, the measured data are distorted due to incomplete development of material expansion. In order to systematically study the influence of ambient temperature T A on the test accuracy of the HLS, a test platform was built in the ambient temperature laboratory, and the influence of factors, including the amount of T A change, the rate of increase/decrease of T A, the expansion coefficient of the connecting pipe, and the distance of the measuring point, on the HLS test accuracy was quantitatively analyzed. Hydrostatic levelling system (HLS) is widely used to monitor the settlement of major projects, such as high-speed railways, bridges, tunnels, dams, and nuclear power plants ambient temperature is the most important influencing factor in the actual engineering settlement detection process.