Abstract: With the development of electronic industry, micro solder joints require higher and higher reliability. The Sn-0.3Ag-0.7Cu-xLa joints were obtained by reflow soldering, with Sn-0.3Ag-0.7Cu as the substrate and different contents of La. The effect of La on nano mechanical properties of the soldered joints was studied. The mechanical performance parameters of joints, nano indentation hardness H, elastic modulus E and creep strain rate sensitivity index m, were obtained through Ma geophysical inverse analysis method based on the force-depth data. The results show that the values of hardness and elastic modulus had an obvious tendency of increase with the increase of La content. And the creep resistance of solder joints was improved with the increase of La content.