In order to further achieve high efficiency and high precision forming of sand 3D printing， the study investigates on normal vector and unitisation preprocessing of sand stereolithography （STL） model， extract the internal contour of multi-contour sand model of complex structure， and put forward the adaptive layering thickness criterion of the unit normal vector | Z | maximum of triangular faceted slice in each layer of sand 3D printing， so as to achieve the high-precision layering of the STL model taking into account of different curvature profiles in both the printing direction and the horizontal direction. Finally， based on the MATLAB development platform， we write a multi-profile adaptive test program for sand model， and carry out the slicing test on the complex pump casing sand/core STL model. The experimental results show that the adaptive slicing algorithm can significantly improve the forming accuracy of the sand printing and forming efficiency at the same time. The study has great theoretical value and engineering significance for sand 3D printing.