Abstract: Modulation transfer function (MTF) is one of the important indexes to evaluate the image quality of infrared electro-optical imaging system. The testing principle of MTF test by tilting target (slit or knife-edge) was detailedly analyzed, and the contrast test about the two methods was carried out. An improved knife-edge method was proposed, multiple rows of data knife-edge were aligned and arranged in a row of data as a edge spread function, which could significantly increase the simpling points, improve simpling rate and testing resolution, and the knife-edge image was obtained. Line spread function (LSF) of each row was got by differentiation, the MTF of the new image composed of LSF multiple rows of data was calculated by canted slit method. Experimental results indicate that, the proposed method is simple and can effectively reduce the noise impact during MTF test process, the difference of the test result is not more than 7.5% compared with the canted silt method.