Abstract: A photo electric track system for a spherical robot is designed, which utilizes the spline interpolation method to estimate the trajectory of the robot via the 1st and 2nd condition as interpolation boundary. Under the certain photo electric units, some virtual detection points are added to reduce the detection errors and the cost and improve the accuracy of detection system. Furthermore, the robot can track follow exactly even if the trajectory is out of the detection region. Results show that the proposed method is effective practically.