Abstract: Welding experiments of 8 mm thick plate horizontal butt joint and 6 mm thick plate flat angle T-joint were carried out by OTC arc welding robot. Influences of groove root gap,welding gun angle,arc voltage,welding current and welding speed on formation of butt weld in the root pass,width and reinforcement of back weld,as well as influences of welding speed,arc voltage and welding current on formation of weld,foot size and convexity of T-joint were emphatically analyzed. The welding parameters were optimized through experiments,and butt joints with well formation of both sides,good fusion,uniformly weld width and weld reinforcement were obtained. According to the test,the width of backside weld was 4. 04 mm and the reinforcement of backside weld height was 0. 17 mm. The width of front weld was 14. 20 mm,and the reinforcement of front weld was 1. 22 mm. T-joints were welded with the optimized welding parameters. The fillet welds were well fused in the area of both toes. The welds were even and slightly concave on the surface. The foot size measured by the test was 6. 8 mm.