Abstract: In satellite navigation satellite clock generator, the phase difference between the master and the slave satellite clocks is measured according to a certain frequency, and the phase difference is regarded as satellite clock monitoring information that is transmitted through a wireless downlink channel.For the proposed long stability test method of orbital satellite clock, satellite clock monitoring information is first demodulated by the ground the receiver; then, the sample values of the phase difference between the master and the slave satellite clock are finally obtained by data processing; the characteristic parameters of the long-term stability of the satellite clock can be finally calculated. The proposed method overcomes the problem of the traditional method requiring high-precision ground frequency reference and complex test equipment. The proposed method is simple and rapid, and the measurement accuracy meets the test requirements. Using the proposed method of multiple navigation satellite in-orbit testing, the test results agree with the results of ground tests before launch for the same satellite clock. The proposed method can accurately reflect the long-term stability characteristics of the navigation satellite orbital clock.