Abstract: In order to promote green products and open up international markets and in response to EU RoHS directive, it is necessary to promote lead-free soldering of circuit boards of nuclear power instrument-controlled products. The lead-free soldering process of nuclear power instrument-controlled products is studied and verified by DOE test, and the inspection and analysis on appearance, metallography, SEM images of lead-free process products are conducted. Effects of temperature and environment on the welding quality are studied. It is confirmed that stable product of good quality can be obtained when the process curve for Sn-3.0 Ag-0.5 Cu welding material is suitable with the peak temperature about 237 ℃ and the holding time about 35 s.