After completion of stainless steel cladding on low alloy steel of reactor pressure vessel,extensive thinning of base material due to excessive defects may induce the structural integrity analysis dissatisfy the requirements. This study completed the design of complex welding repair of low alloy steel base metal and stainless steel cladding,and based on the test plate of reactor pressure vessel base metal（16 MND5）,the simulate welding repair process via manual arc welding and property analysis have been conducted. The analysis show that the base metal and welding repair area are well-fused,and the chemical composition,micro metallography,corrosion,bending,hardness test and non-destructive test results of the welding repair meet the acceptance requirements.