The invention discloses a device and a method for testing a delay index of observing and aiming equipment, and belongs to the technical field of photoelectric testing. The device for testing the delayindex of the observing and aiming equipment comprises a base, a millisecond meter, a plane mirror, a combined prism and a camera. The base is used for fixing tested equipment. A millisecond meter isarranged on one side of the base. The plane mirror is movably arranged on the base. The combined prism is arranged at the front end of an eyepiece of the tested equipment. The camera is placed on oneside of the base, and the camera, the combined prism and an ocular lens of the measured equipment are located on the same straight line. According to the device and method for testing the time delay index of the observing and aiming equipment, the testing speed is high, the tested equipment does not need to specially design a testing interface, the whole machine does not need to be disassembled, testing data is in the same picture, testing is visual, and processing and storage are facilitated. The device has good universality, and positioning and installation can be carried out according to different tested equipment. Only the support needs to be improved, and infrared equipment, low-illumination CMOS equipment, head-mounted display equipment and the like can be tested.