Low-alloy steel electrode CHE608HR is used for support of nuclear steam generator. Adopting PWHT temperature of 620 ℃ with different PWHT holding times,the influence of postweld heat treatment（PWHT） holding time on the mechanical properties and microstructure of weld metal is studied by metallographic microscope. The results show that as PWHT holding time increases,the tensile strength of deposited metal reduces and impact property at low temperature rises at first and then decreases. Wtih the PWHT holding time of 1～24 h,good comprehensive mechanical properties of deposited metal can be obtained.