When a laser beam passes through a strong scattering medium such as white paint or milk, multiple scatterings will occur, thus resulting in the formation of random speckles. In this study, a distribution-estimation algorithm was proposed to focus a beam through a scattering medium via phase and amplitude modulations. The effects of the total number of modulating units and the number of iterations on the focusing effect were analyzed theoretically. Furthermore, phase modulation was performed using distribution-estimation, genetic, particle-swarm-optimization, and continuous sequence algorithms. Subsequently, changes in the light-intensity enhancement factor at the target position were observed. The result shows that, compared with other algorithms, the distribution-estimation algorithm accelerates modulation convergence, enhances noise resilience, and offers superior focusing effects.