The optically soft particles are rich in nature, such as particles in seawaters. Several methods, e.g. Raleigh-Gans theory, Anomalous Diffraction theory were used to deal with soft particles, but they were confined to a very narrow range of refractive indices and were not sufficient for some applications. We employed a new method based on the ray-tracing technique to compute the near field, which was mapped to the far field using the exact diffraction formula and considering the properties of soft particles that only the first several orders of reflection and refraction contribute to the scattering. There are some advantage for this method: firstly, the application range about refractive indices could be extended from 1.01 to 1.2; secondly, this new method is independent of the size parameter, which overcomes the drawback of the conventional geometric optics method. The larger size parameter is, the more rays are needed. The comparison between pseudo-spectral time-domain method(PSTD) and this method shows a reasonable agreement.