To analysis the influence of cladding without preheating on the crack sensitivity of base metal,the alloy content and heat treatment is investigated by cladding test with parameters for actual product,combined with the mechanism of crack occurrence. Research indicates that compared with SA-508Gr.2 Cl.1,content of harden element is reduced and hydrogen is strictly controlled for SA-508Gr.3 Cl.1,which reduces the sensitivity of SA-508Gr.3 Cl.1 to re-heating crack and hydrogen induced crack. Transition cladding of SA-508Gr.3 Cl.1 with preheating and post-heating or stress relieving heat treatment reduces the sensitivity of hydrogen induced crack again. Corrosion-resistant lay of cladding without preheat has little influence on the heat affected zone and base metal. The result of liquid penetrant test and magnetic test indicates that no micro crack exists at the interface of base metal and cladding as well as 3 mm under cladding. The research above concludes that corrosion-resistant cladding without preheating will not increase the risk of under-clad crack of low alloy steel base metal and heat affected zone,reduce the high temperature time for cladding and reduce the probability of hardening phase,which in all make the quality of cladding more reliable.