A 3D printing supporting structure design method based on an STL file comprises the following steps that 3D modeling software is used for conducting three-dimensional modeling on a model, the STL fileis exported, the STL file is read, triangular patch vertex and normal vector information in the STL file is read, a critical angle is defined, the read triangular patch information is integrated, a to-be-supported area is projected to a working plane to form a two-dimensional projection area to obtain a part needing to be supported, sampling point sampling is carried out to generate a supportingstructure, and all vertex coordinates and normal vector coordinates are written into an STL file. Compared with the prior art, the problems that a traditional supporting structure is excessive in useamount, materials are wasted, the supporting structure is difficult to remove, and a to-be-supported area of a sharp-angled model including a suspension edge, a suspension point and the like cannot bedetected are solved, by means of the 3D printing supporting structure design method based on the STL file, the calculation efficiency is improved on the premise of guaranteeing that the model is tender and is consolidated and stably printed, the printing cost is saved, and the supporting structure is easier to remove.