The invention relates to a device for measuring a phase spectrum of a comb-shaped spectrum generator. The device comprises a reference signal output end for outputting a first microwave signal and a signal input end for inputting a comb-shaped spectrum signal synchronized with a femtosecond pulse laser beam, and further comprises a first microwave signal source, a second microwave signal source, a GSG microwave probe, a coplanar waveguide, a femtosecond pulse laser, a wave chopper, a polarizer, an optical delay line, a lambda/2 wave plate, a polarized light compensator, a lambda/4 wave plate, a polarized light separator, a balanced photoelectric detector, a lock-in amplifier, a control and calculation unit and a function generator. The device has the following advantages: the time-domain waveform of the comb-shaped spectrum generator can be accurately measured based on the photoelectric technology, so that the phase spectrum of the comb-shaped spectrum generator is obtained. The device can theoretically measure the comb-shaped spectrum generator with 110 GHz of band width, and has the advantages such as little correction processing and complete tracing chain compared with the traditional method for measuring the phase spectrum of the comb-shaped spectrum generator.