The present invention provides a laser tube window transmittance test device and method. The device comprises: a light source module configured to generate a simulation light beam of a laser of a simulation laser gun; a field diaphragm arranged at one side of the laser tube window and configured to allow the shape of the light spot of the simulation light beam to form a predetermined shape, wherein the predetermined shape is a mark shape of the light beam on the laser tube window; a signal collection module arranged at the other side of the laser tube window and configured to collect the optical signal of each coordinate point position in the light beam mark region of the laser tube window and convert the collected optical signals to electrical signals; and a processor connected with the signal collection module and configured to process the electrical signals to form image information. The laser tube window transmittance test device and method can perform transmittance test for the laser beam mark region on the laser tube window and can perform quantization determination for the transmittance of the region so as to ensure the accuracy of the laser output transmittance.