Taking tube bender system for producing pagoda-shaped fluorescent tubes as an example in this paper, four coordinates movement equations of CNC system with Parabolic characteristic are derived and an algorithm for nonlinear interpolation of four-axis linkage based on target point tracking algorithm is presented for the spiral fluorescent tube bending machine with CNC system by means of deep analysis of the pulse interval interpolation algorithm. By using this algorithm, coordinated control of four coordinates in tube bender system can be realized and, in addition, software programming procedure can be directly used for this system. Test shows that the system which uses this interpolation method has the characteristic of simple operation, high speed and high single-pulse interpolation accuracy.