Under the given build orientation, slice thickness affects the step effect on the surface of the fused deposition modeling part, and slice contour with its hierarchical relationship is the research basis for path planning. An adaptive slice method based on the operation of Boolean volume contours was proposed. Local contour topology was constructed on different height slice-plane of a part model and the kernel region was calculated. Contour loops were mapped to one-dimensional axis according to the intersections of connection lines between kernel points with the contour loops. The hierarchy relationship of contour loops was determined by topological mapping. N-ary tree was built by the hierarchical relationship. The Boolean operation of volume contour with feature change was mapped by the height of the N-ary tree. Adaptive slice thickness was designed according to the slice variation threshold. Volume error under any slice thickness was estimated by the posterior error of volume contour. The effectiveness of adaptive slice was verified by the volume error. According to printing examples and the comparison of different adaptive slice methods, the calculation accuracy of slice volume error obtained by contour posterior error is higher than that obtained by the method of cusp height. Volume error is reduced by controlling slice thickness on the part of volume contour features, and surface forming accuracy on the region of model features is improved with the volume error reduced.