Abstract: A device for measuring the Modulation Transfer Function (MTF) of an optical system, the device including a six-axis manipulator and an internal focusing collimator. The internal focusing collimator is fixedly installed on a flange of the manipulator. The manipulator is used to adjust the exit pupil of the internal focusing collimator and the posture of the internal focusing collimator. The tool control points of the manipulator are set at the exit pupil of the internal focusing collimator. The exit pupil of the focus collimator is located at the entrance pupil of the optical system to be measured so that the exit pupil of the inner focus collimator and the entrance pupil of the optical system to be measured are arranged in parallel. The device uses a manipulator to surround the tool point, only changing the posture and does not change the characteristics of the position transformation.