In this paper, a new automatic test method based on Field Programmable Gate Array (FPGA) is presented. The video information of workpiece is obtained by using the CCD camera, process this information and generate the row synchronization signal and the scene synchronization signal by the synchronous separate circuit, at the same time, generate the binary information of the video signal by the binary decision circuit, then the video graduation module which is realized by the FPGA is used to analyze and process this signal and Figure out the test result. The video graduation technology based on FPGA is researched in this paper, the generation principle of the video vertical line and video horizontal line are introduced in detail, the test principle of video line is explained, the hardware and software design of the test system are given, and the test error of the system is analyzed. This method needs simple circuit, convenient operation, and has high reliability, the system's function is extensible, in addition, it tests rapidly, low-cost and has high precision. The system, which has been implemented in automatic test for the mesh status between wormgear and worm of the induction ammeter, has been tested a lot, and is shown to be able to test the ammeter effectively. Also, this system fits to mass-produced workpieces' dimension test on the product line, and helps to improve produce efficiency and enhances product quality.