Interpolation algorithm is one of the key technologies of NC system,it plays an important role in metal welding forming machine.And the metal parts formed by polar coordinates has high mechanical properties and surface finishing.Considering this,the principle of linear interpolation algorithm of polar coordinates was studied,a new method for judging the end point was proposed to solve the problem of linear interpolation error operation of special points,and the straight line interpolation formula was derived.Finally,the above principles and methods were used to write the software to verify the interpolation algorithm.