Modulation transfer function (MTF) is an important imaging quality indicator of optical system. On the basis of MTF testing theories, knife edge and slit as testing targets, a testing system which has low cost, simple structure, but high precision and high stability is developed to evaluating MTF of industrial lens. Besides, a correlative testing software is built according to the above. This testing software basing on the principles of the automatic focusing, and giving consideration to efficiency and precision, includes an automatic focusing system which rough focusing uses the method of mountain climbing as search algorithm, and which elaborate focusing uses the traditional method as search algorithm. In addition, different focusing evaluation functions are used in sharpness evaluation according to the trait of objective. Experimental data indicates this MTF fast testing system has high stability.