Snow grain sizes retrieval accuracy was affected by many factors wile snow shape was an important factor. Asymptotic radiative transfer (ART) model used a digital simulation and asymptotic technology to simplify radiative transfer models, which was widely used to reverse snow grain. ART model considered two snow shape parameters, which depended on the snow grain shape and asymmetry (considering 3.62 for fractal particles; and 4.53 for spheres particles). In reversing snow grain processing of ART, the shape parameters were determined beforehand, but in nature snow particles might take on different shapes, and ART couldn't accurately reverse snow grain sizes with single shape parameter. In order to accurately reverse snow grain sizes, snow grain sizes and shape parameters must be obtained simultaneously. Based on ART model, a Look- Up- Table Minimal Angle model was proposed to solve the problem. The new model could obtain the shape parameter values and snow grain sizes simultaneously, solving the problem of determining shape parameter value beforehand, which determined the shape parameter values automatically. Experimental results showed that new model could accurately retrieve snow particle sizes, which were more consistent with field validation datas.