Abstract: The quality assessment of GNSS (Global Navigation Satellite System) space signals plays an important role in the design and operation of the system. It is also an essential task in the integrity monitoring of space signals. In this paper, the methodology for evaluating GNSS space signals is first described in detail, which is based on pseudo-range or carrier-phase observations from a GNSS monitoring receiver. Next, the feasibility of the presented algorithm is validated by using a simulation experiment. Furthermore, an experiment on the real BDS pseudo-range measurements is carried out in order to validate the effectiveness of the developed method. The results show that the proposed scheme is highly potential to evaluate the quality of GNSS space signals according to the three metrics, namely original measurements, fitting residuals and standard deviation of fitting residuals. Therefore, the proposed evaluation technique can provide a guarantee and help for the continuity and reliability of GNSS space signals.