Abstract: The smoothing method based on the heat diffusion has a good effect to the point cloud with noise points, but how to choose a proper disciplinal function to smooth the point cloud is no answer. This paper proposed a method to decide the disciplinal function based on the fuzzy mathematics’s relevant function concept. The six special functions, such as drop semirectangle function, drop semiГ function, drop seminormal function, drop semiCauchy function, drop semitrapezia function and drop semimountain function, were analyzed. The answer was gotten that the variant has a nonlinear relationship with the result of disciplinal function. Some cases were used to validate the characteristics of disciplinal function. There is a new way to handle the point cloud during the preprocessing of reverse engineering or complex surface inspection.