Welding process test of 6 mm pure nickel N6 plate is carried out by plasma arc welding（PAW）. Based on a large number of technical tests by orthogonal design in earlier period,the welding parameters are optimized with statistical product and service solution software（SPSS）. The results show that single pass double formed welding joint of 6 mm pure nickel N6 plate can be achieved by PAW. Welding current has the most significant effect on tensile strength of joint,followed by plasma gas flow and the third is the welding speed. So optimal process parameters obtained by orthogonal test design are as follows:welding current 175 A,welding speeding 170 mm/min and plasma gas flow 1.5 L/min. Average value of tensile strength of joint welded by those parameters can reach302 MPa,which is up to 87.3% of the strength of base material and above result illustrate that the parameters obtained by orthogonal test design are reliable.