It is proposed that the diffraction theory of aberration be used to evaluate approximately the optimal focused area of a high-power laser and the intensity distribution at the focused area. In one proposed method, the phase distribution of the laser beam is yielded by processing the interference fringe obtained from the front of the focal lens of the laser system. The amplitude distribution can either be assumed as super-Gaussian in shape with low frequency modulation, or can be simulated by computing the laser propagation using an FFT algorithm with real samples. In another method, the irradiation distributions are demonstrated experimentally using hologram reconstruction. This method can provide more details of the focused laser beam than digital computation.