The invention provides a device for avoiding damage of stray light to an underwater laser detector. The device comprises a Q-switched device; a signal light receiving window which is arranged on the coaxial light path of the Q-switched device; a signal receiving device which is arranged on the coaxial light path of the Q-switched device and the signal light receiving window and is positioned behind the signal light receiving window; a photoelectric analysis/control module which is arranged on the coaxial light path of the Q-switched device and is positioned behind the signal receiving device; a detection laser emitting window which is arranged on the direction of the signal light receiving window and a normal line, i.e. the detection laser emitting window is parallel to the light axis of the signal light receiving window; a pulse laser source which is arranged on the coaxial light path of the detection laser emitting window; and a waterproof shell in which the signal receiving device, the photoelectric analysis/control module and the pulse laser source are accommodated. The objective of the invention is to provide the device for avoiding damage of stray light to the underwater laser detector, the photoelectric analysis/control module and the pulse laser source work in a linkage way so that the device for avoiding damage of stray light to the underwater laser detector has advantages of being economical in price, simple in structure and flexible in application.