Angular spectrum method has distortion problem in the long-distance diffraction calculation because of the calculation error caused by the reduction of effective spectrum components and spectrum aliasing. Based on the frequency sampling characteristics of the band-limited angular spectrum method, an improved scaling angular spectrum method is proposed. Then, the method is applied to the diffraction field simulation of large-size square telephoto lenses, circular axicon lenses and diffractive optical elements. The results show that compared with the original band-limited angular spectrum method and the scaling angular spectrum method, the diffraction field obtained by the improved method has higher resolution and no edge distortion. Our research indicates that the improved method has important application potential in the precise calculation of large size, long distance and small diffraction fields.