The invention discloses an underwater light source device with a hairbrush and a diaphragm for an underwater optical experiment with a light source. The underwater light source device comprises a light source, a stepping motor, a rotary shaft, a diaphragm system and an oscillating bar. The rotary shaft is connected to the output shaft of the stepping motor, the oscillating bar is arranged on the rotary shaft, and the rotary shaft rotates to drive the oscillating bar to control the diaphragm system to be turned on and off; the diaphragm system is attached to the light source for controlling illumination of the light source to pass through and to not pass through and clean the surface of the light source. The underwater light source device disclosed by the invention effectively avoids dangers due to instable working state as the light source is turned on and off when the power of the light source is relatively great (greater than 100W) and relatively large current on and off, the time required by waiting the working state of the light source to be stable is shortened, and the experimental efficiency is increased. Moreover, the surface of the light source is immediately cleaned to prevent attachments such as water drops and floats on the lamp wall from affecting illumination, so that the result obtained from the underwater experiment is more accurate and the experimental flow is safer.