Abstract: A surface quality evaluation method based on 3D surface roughness parameters was proposed for the forming problem in wire and arc additive manufacturing. Multi-bead overlapping samples of high nitrogen steel were deposited by CMT additive manufacturing, and the surface information was extracted by 3D scanning equipment to calculate the surface profile root mean square deviation S_q and profile skewness S_sk for comparing the data with the actual surface forming. The effect of swing arc on the surface quality of arc additive forming was investigated by this method. The results showed that the data obtained by this method was basically consistent with the actual situation. The evaluation method had good adaptability and scientificity. The forming surface quality can be divided into four grades: A, B, C and D from excellent to bad based on Sq and Ssk. The heat input and arc swing amplitude have great influence on the surface quality. Under the high heat input, when the swing arc amplitude is 15 and 10 mm, the overlapping forming surface with swing arc is better because of the small deposition height and high width to height ratio.