Based on angular spectrum diffraction theorem and circular Gaussian distribution model of scattering media, light focusing through scattering media was numerically simulated. A high contrast focus in the target area is produced by using a feedback optimization algorithm to shape the wavefront of the scattering light. By adjusting the target area, it is also possible to form one or multiple foci at will. The influence of the number of square segments of the spatial light modulation and the phase precision of a single segment on the intensity enhancement was discussed. The result shows that the light intensity at the target area increases linearly with the increasing number of square segments of the spatial light modulation, and becomes stronger with the increasing phase precision.