A semi-analytical method of rapidly estimating the maximum communication distance of an underwater laser communication system is proposed. For a given underwater optical channel, only two simulation times are needed to obtain the maximum communication distance. Once the system conditions are changed, no more simulations are needed. Two reference distances through simple mathematical operations based on the parameters of underwater optical channel are initially deduced. Than a separate simulation is conducted for each reference distance. Finally, an equation for calculating the maximum communication distance is deduced based on theoretical analysis. The simulation results are compared with experimental ones and are found to coincide well with each other. The validation of the semi-analytical method is proved.