Sn-0.7Cu and Sn-0.7Cu-xGe solder alloys were prepared to investigate the in uence of trace Ge on liquid Sn-0.7Cu lead-free solder at high temperature. The spreadability and the wetting force of solders were tested, and the oxidation-resistance was also evaluated by eye observation and skimming at 250 C 370 C. The results have shown that trace Ge can improve the spreading rate of Sn-0.7Cu, but have a few effect on the wettability. The oxide slag quantity of Sn-0.7Cu was three times more than the Sn-0.7Cu-0.012Ge at the same temperature and period, the optimal content of Ge to improve the oxidation resistance of Sn-0.7Cu was 0.012 mass%. The growth factor of oxide lm on the surface of liquid Sn-0.7Cu solder (k 250 C = 1.59 × 10 −6 , k 370 C = 3.03 × 10 ) at 250 C and 370 C respectively.