A new adaptive background correction method based on pinhole image analysis in optical system modulation transfer function (MTF) measurement is proposed. The pinhole image is got from the CCD, and the line spread function is computed from it. The MTF is got from the adaptive background correction to the line spread function. Compared with the traditional background correction method, it is unrelated to the change of ambience illumination, and the measurement accuracy is improved. Standard lens and aberrated lens are tested to prove the validity of the adaptive background method. The maximum difference between the test results of standard lens and the academic results is 0.01. Compared with Optikos MTF testing results, the maximum difference is 0.015. The maximum difference between test results of aberrated lens and Optikos MTF testing results is 0.013. The test results show that the adaptive background correction method is practical to the MTF tests of most optical lenses.