Aimed at the short working distance and the low target image quality problems of synchronous scanning trigonometric ranging underwater laser imaging system caused by scattering and absorption,a stochastic model of underwater laser transmission is established by using Monte Carlo method based on the radiation transmission theory.The influence of target distance,laser intensity,baseline distance and objective caliber on the contrast quality of laser illumination target reflection image is discussed using TracePro,and the system parameters are optimized.Finally,based on the actual situation and needs of the system,the laser light intensity of 1 W,baseline distance of 250 mm,and the lens specification 50 mm /F2 are determined to ensure a better image contrast of target reflection point within the range of 7.5 m,thus ensuring the implementation of the synchronous scanning triangulation principle.