Abstract: A new Sn-9Zn-2.5Bi-1.5In solder is prepared, a wave soldering nitrogen protection system is developed, and the soldering quality of the solder under different oxygen content is investigated. The results show that the modified nitrogen protection system can reduce the dynamic oxygen content to less than 0.06% by increasing the nitrogen flow. Reducing O₂ content in the soldering zone can significantly decrease the number of bridging, poor filling and pore defects, and the failure rate is controlled within 0.20%. Under the critical value of 0.50% oxygen content, the joint can be soldered at low temperature under the condition of 225 ℃ setting temperature. The soldering quality can meet the needs of large-scale production. EDS analysis shows that the content of Zn in the oxide dregs is increased by 84.9% compared with the original Sn-9Zn-2.5Bi-1.5In alloy, and the easy oxidation tendency of Zn leads to the formation of a large number of oxide slags. Reducing the oxygen content in the soldering zone can restrain the formation of oxide slags on the wave's surface. Nitrogen protection can solve the soldering defects of Sn-Zn alloy to realize low-temperature wave soldering at 225 ℃.