The modulation transfer function (MTF) is an important parameter for evaluating the imaging ability of an infrared focal plane (FPA) for targets with different spatial frequencies. The MTF of the focal plane is affected by the size of the photosensitive area of the pixel, center distance of the pixel, and carrier diffusion length. As the number of pixels decreases, the influence of the carrier diffusion length on the MTF becomes more evident. In this study, a convenient and accurate MTF testing method was designed to meet the requirements of MTF testing for hybrid FPA. A special microstructure was fabricated on the focal plane through metal deposition, photolithography, and other processes to replace the inclined knife edge. The MTF of the FPA was obtained by the proposed infrared focal-plane test method. The results demonstrate that the MTF of the FPA can be measured accurately and conveniently using this method, which is convenient for FPA production and development companies to evaluate the FPA performance and verify device fabrication quickly.