A simulation model of underwater Gaussian beam transmission by Monte Carlo method was established, and the influence of receiver tilt angle and receiver position on the attenuation of received optical power based on this model was emphatically studied. The simulation results show that in the underwater channel, the received optical power reaches the maximum when the receiver array is correctly aligned the laser beam, and the received optical power gradually decreases with the increase of the receiver tilt angle. When the receiver moves forward along the Y-axis, the received optical power remains unchanged when the receiver is within the diameter of the laser beam. When the receiver is outside the diameter range of the laser beam, the received optical power decreases with the increase of the distance from the origin of the receiver. The simulation results can provide reference for the practice of underwater laser communication engineering.