The invention relates to the technical field of photoelectric transient state testing and provides an optical control system, a control method and a laser Doppler velocimeter. The optical control system includes an optical power reference value input module, a reflected light power detection module, a controller and an optical power adjusting module. According to the technical scheme provided by the invention, dynamic adjustment of emitted light power can be performed according to the change of reflected light power, so that the reflected power is kept constant and is equal to or in a fixed proportion with the reference light power; amplitude stability and base line stability of coupling interference signals of reflected light and reference light can be ensured; a condition that a to-be-detected object can reflect light of sufficient power can be ensured; testing signal quality can be improved; signal-to-noise ratio of signals can be improved; and a phenomenon of signal loss caused by too weak reflected light can also be inhibited; and the testing reliability is improved.