We propose a method of the combination of splicing and fusion based on the complex surface triangular mesh of karst caves. First, the two boundaries of the mesh to be spliced are found by traversing the spatial geometric relationship of the triangular mesh. Second, the constrained Delaunay triangular mesh method is used to connect different meshes and the B-spline interpolation is used to make the connection transition natural. Finally, the Laplacian principle is used for smoothing and eliminating the peaks to smoothen the edges. Experimental results show that the proposed method can achieve high-efficiency automation in the splicing and fusion of the triangular mesh of karst cave and can reduce human interventions. After the completion of splicing and fusion, the triangular mesh can be exported for the subsequent engineering design, which could be used as a reference for the development of engineering applications.