In order to achieve the big image plane，small throw ratio，high definition picture requirements，a catadioptric ultra-short focal projection lens is designed. According to the requirements of performance indicators，the inverse telescopic system is selected，and the initial structure is obtained by the scaling method. The mirror coordinate data is obtained by calculation from the relationship between the light rays of different fields of view and the height of the image plane at the exit pupil position，and the mirror surface type is obtained by fitting. The image quality is evaluated by using point plot， field curve/distortion and modulation transfer function（MTF）curve. Finally，an object-space telecentric system with a focal length of 5.45 mm and a throw ratio of 0.4 is obtained. When the projection distance is 720 mm，it projects an 80 inch screen with a resolution of 1 080 p，a field of view of 136°，and a magnification of about 125 times. The RMS radius of the column diagram is less than 750 μm，the distortion is less than 0.2%，the relative illuminance is above 96%，and the MTF curve amplitude is greater than 0.3 at 0.54 lp/mm. Tolerance analysis shows that the system design is reasonable and the imaging quality is good. Compared with other catadioptric ultrashort focal projection lenses，the system can ensure the imaging quality without using aspherical surface in the refraction part，which effectively reduces the difficulty of processing and assembly.