Abstract: By optimizing the thickness of salt tube and the material of intermediate gasket in the assembly structure of PCBN composite layer, the effects of the thickness difference, the hardness of the same position and the overall wear resistance of the polycrystalline layer were investigated under the four conditions of no optimization (A), optimization of intermediate gasket material (B), optimization of salt tube thickness (C) and joint optimization of the intermediate gasket and the thickness of salt tube (D). The results show that when the thickness of salt tube changes from 1.0 mm to 1.4 mm, and the intermediate gasket material changes from graphite to cemented carbide, the hardness and overall wear resistance of the polycrystalline layer of PCBN composite are basically unchanged under the four conditions. At the significance level of 0.05, B, C, D optimization relative to A, D optimization compared to a single factor B and C optimization, can improve the uniformity of the thickness difference of polycrystalline layer. The optimization of B, C, and D is relative to that of A, and the optimization of D is relative to that of C, which can improve the stability of the thickness difference of the polycrystalline layer. However, the D optimization compared with the B optimization does not improve the stability of the thickness difference of the polycrystalline layer.