The transmission characteristics of laser in four types of harbor water were studied using Monte Carlo method simulations for the characteristics of strong absorption and high scattering of water in marine harbors. The effects of water quality parameters and transmission distance on the optical signal power, impulse response and spot quality were quantified and analyzed at certain optical wavelengths, optical energies and divergence angles. The analysis shows that the attenuation characteristics of laser remain consistent as the attenuation length increases when the optical signal is transmitted in the four types of harbor waters. The rate of attenuation of the optical power also does not conform to the linear relationship described by Beer's law. Under the same water quality conditions, the width of the optical pulse, the size of the light spot increases with the attenuation length. However, when the attenuation length is transmitted from 20 to 30, the width of the optical pulse is almost unchanged, and the change in the amount of light pulse spreading is less than 1 ns with the size of the light spot increases continuously. In addition, at the same attenuation length, the light pulse and the spreading amount of light spot with the water quality attenuation coefficient increases and decreases.