Disclosed is a positioning device for radiotherapy. The positioning device comprises: a bed board for fixing a patient; a mechanical arm with six degrees of freedom, which is connected to the bed board and used for adjusting the position of the bed board; a position detection device, which can be used for detecting the distance between people or objects in an environment where the bed board and the mechanical arm with six degrees of freedom are located so as to obtain position information; a torque detection device, which is disposed between the bed board and a bed board adjusting assembly and used for obtaining torque parameters of the bed board in various directions; and a controller, which is used for communicating with the mechanical arm with six degrees of freedom, the position detection device and the torque detection device so as to control the mechanical arm with six degrees of freedom to adjust the position of the bed board according to the position information and the torque parameter. Therefore, the position detection device and the torque detection device are arranged to improve the stability and reliability of the bed board adjustment process and shorten the time required for positioning the bed board, thereby improving the treatment efficiency.