Modulation transfer function (MTF) can be used to evaluate the image quality of high resolution optical satellite sensors. On-orbit MTF detection is significant to the application of high resolution satellite remote sensing data and the development of future satellite sensors. A directly detection method based on reflected point source is presented, and the point spread function (PSF) and MTF value are obtained based on remote sensing image data. According to the imaging relationship and point source imaging data, the one-dimensional line spread function value of optical satellite sensor imaging system can be acquired by way of solving non-linear equations. Additionally, the Gaussian model which is usually used to characterize the PSF of high resolution optical satellite sensor is also verified. The results show that the difference of on-orbit MTF detection results of optical satellite sensor based on reflected point sources is less than 5% compared with that of the method based on knife-edge tarps. The proposed approach can achieve on-orbit MTF detection for high resolution optical satellite sensor.