Abstract: Thermodynamic calculation and evaluation for Sn-Ag-Cu-Ce lead-free solder alloy system were carried out by means of Chou model.The results showed that chemical balance attained in the system of Sn(rest) Ag(0.5 wt.%-4.5 wt.%) Cu(0.5 wt.%-4.5 wt.%) when the content of Ce was over 0.05wt.%.The equivalent activity coefficient phenomenon of Sn,Ag and Cu emerged in the system when the content of Ce increased to about 0.6wt.%.The results will provide theoretical guidance for designing chemical constitutions of new lead-free solders.