Based on the structural characteristics of the ankle joint and the great demand for ankle rehabilitation robots in the current market, a simple and practical 3-degree-of-freedom 2-UPS/RRR parallel mechanism is proposed based on the analysis of the existing ankle rehabilitation robot mechanism for traditional ankle rehabilitation and other problems. The design of the constrained support chain and moving platform ensures that the rotational centers of the mechanism coincide with the rotational centers of the ankle joints of different patients; firstly, a degree of freedom analysis is carried out using the Kutzbach-Grubler degree of freedom formula, which leads to the conclusion that the robot has 3 rotational degrees of freedom; secondly, the closed-loop vector method is used to obtain the inverse equation of the robot's position; and finally, the boundary search method is used to solve the workspace, which shows that the robot has three rotational degrees of freedom. Finally, the boundary search method is used to solve the workspace, which shows that the robot meets the requirements of ankle rehabilitation range of motion. The results show that the range of motion of the designed ankle rehabilitation mechanism can meet the demand of human ankle rehabilitation.