Abstract: In order to solve the problem that the traditional contour filling algorithm may cause internal defects, the filling algorithm of slice contour based on straight skeleton was studied. Firstly, a simplifying algorithm was applied to the slice contour. Then, the calculation of straight skeleton of the pre-processed polygon contour was carried out, and all the straight skeleton line strings was extracted, which were composed of internal bisectors in the half-edge data structure of the straight skeleton extraction results. After the line string buffer operation and polygons union operation, the first offset result was obtained. Finally, the offset filling tool path of thin-walled parts based on straight skeleton was obtained by using the contour parallel offset algorithm. The proposed algorithm solves the problems of possible internal defects caused by the improper filling path of traditional additive manufacturing thin-walled parts.