The welded joint specimens are obtained through surfacing the Cr-Ni stainless steel on Q235 by ESW（electro-slag welding） with band-electrode. Metallographic observation shows that there is various microstructure morphology in the fusion zone,where an "island" and a "peninsula" images are observed. The composition characteristics of fusion zone across the "peninsula" are analyzed by EDS. The formation mechanism of "island" and "peninsula" is analyzed from the metal transfer and molten pool characteristics of electro-slag surfacing. Metallographic analysis of the surfacing layer shows that the welding heat input and cooling rate are the main factors affecting the surfacing microstructure morphology. With the decrease of welding heat input and the increase of cooling rate,the content of δ ferrite in the deposited metal increases gradually, and its morphology changes from vermicular and intermittent to slender skeletal, finally appears dense and thick skeletal and lathy.