Abstract: A trajectory planning method based on PH (Pythagorean Hodographs) curve is proposed to solve the problem that the trajectory of Delta parallel robot in Cartesian space is not smooth when performing high-speed operations. The pick-and-place operation trajectory is determined by applying the PH curve to smoothing the transition portion between the vertical movement and the horizontal movement. The position of the trajectory interpolation point is determined by the trajectory planning for the one-dimensional curve displacement based on the polynomial motion law. In order to minimize the movement cycle time of the pick-and-place operation, the PH curve parameters are optimized to smooth the motion trajectory. The simulation results show that the pick-and-place operation can be completed with a short period, smooth trajectory and stable motion by the proposed method. The experimental results show that the maximum pickup speed is 90 times per minute, which achieves high-speed operations of parallel robots.