As a novel way for the joint of thick plate stainless steel, multi-pass laser welding with narrow gap and filler wire can improve the welding efficiency, but seldom research has conducted to the microstructure of this method. In this article, 304 stainless steel plate with 16 mm thickness are welded by CO2 laser welding with filler, the microstructure of joint are analyzed by optical microscope, electron backscatter diffraction (EBSD) and energy dispersive spectrometer (EDS). The results show that, fine joint without crack and porosity can be obtained by 8 kW laser power and three pass of welding. The welding seam profile is narrow and high with homogenous width from bottom to top. The heat affected zone (HAZ) is very narrow and no coarse austenitic grains are seen beside fusion line. Two profiles of ferrite such as skeletal and equiaxial exist in welding seam. The characteristic of austenitic is mainly columnar grains and the size is very coarse. There is no obvious change in the area near re-melted region in spite of the re-heating of multi-pass laser welding. The main alloy elements Cr, Ni are distributed evenly in welding seam and no obvious segregation are seen.