Abstract: The influence of welding parameters on the microstructure and properties of the friction stir welded joints of dissimilar metals L6 LYI2 was investigated. Signal noise ratio orthogonal experiment and analysis of variance were utilized. The parameters in the order of significance are: pressure, welding speed, rotational speed. The experiments conducted on L6-LYl2 with the thickness of 5 mm by friction stir welding suggest that the pressure can range from 2000 N to 3000 N, the welding speed can range from 37.5 mm to 60 ram, and the range of the rotational speed is 950-1500 r/min. The optimized parameters are 2500 N, 37.5 mm/min and 950 r/min. The welded joints are of homo-strength or hyper-strength.