Abstract: In order to improve the illuminance of image plane and simplify the structure of digital high-speed multi-frame gated camera, an off-axis optical system was proposed. The system uses several same lenses, one of them lies in the center of circle and the others are equally distributed on the circumference. In order to obtain the same image with the center lens, receivers of the lens that are distributed on the circumference parallel move away from the axis of its lens. The illumination, distortion and other aberration related with field of view, were analyzed. Based on the above analyses, a five-channel off-axis optical system was given. The spatial resolution of the system is better than 30 lp/mm , distortion is less than 0.1%. and F number of the lens is 2.0. Compared with mostly used prism or pyramid to split light beams, the illumination of the new system increases more than 5 times and the structure is more simple.