Frequency change system group delay test method

The invention relates to a frequency change system group delay test method which comprises the following steps of: generating an FM (Frequency Modulation) carrier signal of which the carrier frequency is the center frequency of a working frequency band of a frequency change system by a signal source; then dividing the signal into two paths, wherein one path of signal is input to the frequency change system by an attenuator and used as the input of a first A/D (Analog-to-Digital) converter by the attenuator after being output by the frequency change system, the other path of signal is used as the input of a second A/D converter, and the two A/D converters synchronously sample data by using the same reference clock; then respectively carrying out Hilbert transformation, digital down conversion and non-coherent demodulation on two paths of A/D sampled data; and carrying out digital phase comparison on the two paths of demodulated base band signals to obtain a group delay value of the frequency change system. A group delay test result of all frequency points of the frequency change system in the frequency band can be obtained by changing the carrier frequency of the FM carrier signal in the working bandwidth of the frequency change system and repeating the processing; and the measuring precision depends on system heat noise, the correcting precision of a test cable and A/D sampling resolution.