The invention relates to a semiconductor laser broadband frequency locking method and frequency locking device. The frequency locking device comprises a slave laser, a slave laser temperature control module, a slave laser injection current control module, a slave optical isolation module, a slave polarization control module, a master laser, a master laser temperature control module, a master laser injection current control module, a master optical isolation module, a master polarization control module, an optical difference frequency generation module, a photoelectric conversion module, a difference frequency measurement module and a processing module. The semiconductor laser broadband frequency locking device, disclosed by the invention, can reduce frequency jitter of difference frequencies of the master laser and the slave laser caused by power supply noise efficiently, has a more flexible frequency adjusting way and a bigger frequency adjusting range, reduces adjusting difficulty, and has lower cost.