A series of reserved TIG welding experiments are carried out on a 3 mm thick 304 stainless steel plate. A clear image of the front fusion hole is captured by the CMOS vision detection system. By MATLAB image processing tool,the image processing algorithm in line with the characteristics of the fusion hole image is designed,the fusion hole-gap edge is gained,and the widths of the fusion hole and gap are calculated. The results show that the welding parameter window with stable fusion hole is relatively narrow,and the fusion hole can only maintain 4～5 s without adjustment in most cases. When the welding speed is constant,the welding current and the reserved gap are the important factors affecting the size of the fusion hole. Other parameters remain unchanged,the width of the fusion hole increases as the welding current increases;the width of the fusion hole also increases as the reserved gap increases,and shows a similar change rule.