The invention discloses a time-optimal trajectory planning system and method for robot path tracking. The system comprises a path processing unit, a trajectory planning unit and an instruction generating unit. The path processing unit performs path displacement calculation processing, path function fitting processing, path differential coefficient calculation processing and path planning point selection processing. The trajectory planning unit is used for planning an optimal trajectory. The instruction generating unit is used for generating a control instruction and the like. Besides, the method comprises the following steps: S1, carrying out path displacement calculation processing; S2, acquiring a path function; S3, carrying out path differential coefficient calculation processing; S4, selecting a path planning point; S5, calculating a path boundary speed and acceleration of the planning point; S6, planning a time-optimal trajectory; S7, acquiring each control period path displacement; S8, acquiring angular displacement of each axis at each moment; and S9, converting the angular displacement of each axis into a control command pulse signal and the like. Therefore, the path tracking time and computation time of trajectory planning are shortened.