Abstract: At present, the lead-free solders used are mainly binary or ternary Sn-based eutectic or near-eutectic alloys in the field of electronic packaging, and the matrix phase is Sn-rich phase. In order to obtain the mechanical properties and stress-strain relation of the Sn-rich phase, the elastic modulus E and the hardness H of the Sn-rich phase were obtained by nanoindentation test, and the load-displacement curve was obtained. Then, the representative stress and representative strain of the Sn-rich phase are determined by the finite element reverse analysis method, and the strain hardening exponent n was determined by the dimensional function. Finally, the above parameters were substituted into the power-law stress-strain behavior model, the yield strength of Sn-rich phase was calculated to be 31.51 MPa, and the expression of stress-strain relation function of Sn-rich phase was finally determined.