The invention discloses a flexible DC starting loop differential protection test method based on phase compensation. According to the method, when transmission of an AC analog voltage and current signal and a digital FT3 message voltage and current signal is synchronously controlled through the upper computer software, the actual transmission time difference T of the two signals is calculated every second and synchronization of the two signals is realized by using the method of phase compensation on the analog control signal so that synchronous output of the AC analog voltage and current signal and the high-speed digital FT3 voltage and current signal can be realized, and a new method can be provided for the timing maintenance work of the starting loop differential protection logic scene of the flexible DC control protection device.