Abstract: A new composite porous structure with negative Poisson's ratio was designed based on the chiral structure and concave structure. The composite structure samples were prepared with Ti6Al4V spherical powder by selective laser melting forming technique. The effects of ratio of cell length to ring diameter (0.7—0.9), rod diameter (0.4—0.6 mm), concave angle (60°—80°) and their interactions on the elastic modulus and yield strength of the samples were analyzed by response surface methodology, and the cell structure parameters were optimized. The results show that when the porosity was 75%, the elastic modulus and yield strength of the composite structure sample were between those of the chiral and the concave structure samples. The elastic modulus of the composite structure sample was low when the ratio of cell length to ring diameter and rod diameter were small, and the concave angle was larg. The yield strength was high when the ratio of cell length to ring diameter and rod diameter were larg and concave angle was small. The optimization parameters of the composite structure were listed as follows: ratio of cell length to ring diameter of 0.9, concave angle of 60.1° and rod diameter of 0.546 mm. The predicted elastic modulus of the optimized composite structure sample was 3.71 GPa, and the relative error to the test value (3.65 GPa) was 1.64%, indicating that the model of relationship between negative Poisson's ratio structure parameters and mechanical properties established by the response surface methodology was reliable. The measured yield strength of the optimal composite structure sample reached 210.36 MPa.