Lanzhou, located in China's major earthquake belt, is China's most earthquake-proof city. In this region, one of the most important earthquake parameters——shear-wave velocity——always involves a certain degree of test error. This test error can greatly impact seismic evaluation results. In this study, our objective was to develop basic guiding error-analysis principles for Lanzhou and the Northwest China region. First, we selected four test sites in Lanzhou, and then developed a specific in-situ shear-wave velocity test involving ten institutes and various kinds of test equipment to determine the actual in-situ test error in the Lanzhou region. In this paper, we discuss the statistical characteristics of this error and determine its impact on the surface accelerated response spectra. Based on our results, we can draw the following conclusions:(1) The in-situ test error in the Lanzhou area has obvious regularity, which mostly obeys the standard normal distribution. This error remains consistent and does not vary with depth or type of site. (2) The technical level of the Lanzhou region is better than the average level over the whole of China. Its Class I, Class Ⅱ, and Class Ⅲ test errors are smaller and the average standard deviation of the test is 10%. (3) For the Lanzhou area, the test standard deviation of one time of shear-wave velocity could cause a maximum change in the peak ground acceleration (PGA) of 25%, and the standard deviation of two times of shear-wave velocity may result in a change of up to 50%. (4) The calculation results are also influenced by the input ground motion. When the frequency of the input wave has a frequency band similar to that of the site, the spectra will have more vivid differences, and otherwise the impact is lower.