In underwater optical wireless communication (OWC), the impacts of water scattering on divergence angle and distribution of optical power are usually out of consideration in previous studies of receiving optical power. A three-dimensional distributing model for optical power is studied using the Hankel transform of the beam spread function (BSF). Considering the geometrical wastage induced by receiver size, spatial position and receiving angle, the receiving optical power is obtained based on the distribution. Experimentation is implemented, which verifies that the method shows a better agreement with experimental data than previous methods.