The invention relates to an illumination uniformity tester and a test method. The tester comprises a sliding rail, a sliding block, an optical detector, a first motor, a second motor, a base, a controller and a data collector, wherein the first motor controls the sliding rail to rotate by taking a motor rotating shaft as a center; the motor rotating shaft is located at the light spot center of a sun simulator, and the rotating plane of the sliding rail is located at the irradiation surface of the sun simulator; the second motor controls the sliding block to move on the sliding rail along the radial direction; the controller is used for sending a motor control instruction to the first motor and the second motor; and the optical detector is installed on the sliding block and used for measuring the light intensity and sending the measured light intensity to the data collector. The tester can realize the testing for multiple measurement points in the irradiation surface by only one or twooptical detectors through combining the rotation of the sliding rail along the circumferential direction and the movement of the sliding block in the radial direction, improves the measurement accuracy and is particularly applicable to illumination uniformity testing for the sun simulator with a large light spot size.