Abstract: The effects of tempering temperature on microstructures in STE355 steels after welding has been investigated. The simulated weld HAZ specimens were produced by applying single-pass and multi-pass welding thermal cycle respectively with a peak temperature of 1320℃.then were tempered by soaking for 1. 5 hours at 500-620℃ The microstructure changes in specimens,especially the decomposition and transformation of granular bainite and M-A constituent at different tempering temperature were observed by scanning and transmission electron microscopes. The relative proper tempering process was proposed according to the relation between microstructure and properties.