Automatic focusing system and method thereof of OTF (Optical Transfer Function) tester

The invention discloses automatic focusing system and method thereof of an OTF (Optical Transfer Function) tester. The automatic focusing system comprises an image acquisition module, an automatic focusing mechanical module and an analysis and processing module, wherein the image acquisition module consists of a conjugate optical system and an image acquisition card; the automatic focusing mechanical module comprises an interface circuit, a drive circuit, a stepper motor and a mechanical drive device; and the analysis and processing module mainly consists of a computer and OFT test software corresponding to the computer. The invention has lower cost and wide applicability, and compared with manual focusing, the automatic focusing greatly improves the testing efficiency; the automatic focusing mode and the manual automatic focusing mode can be freely switched through rotating a plane mirror; a CCD (Charge Coupled Device), a Carl Zeiss lens, and the like with high resolution and sensitivity are adopted so that the quality of an acquired image is higher, and the testing precision is improved; and the testing operation is finished by one key, thus the automation degree is high.