Light leak degree is one of the most important parameters of piston ring. To make the automatic measuring instrument of piston ring light leak degree more precise and realtime, and solve the problem of rotation winding of camera wire, an embedded system based on FPGA and DSP is designed. The paper introduces the overall design scheme, and hardware & software architecture of the system. Combined with an angle encoder to provide external trigger signal, a wireless transceiver to transmit instructions and datas with computer, and a rotation connector to supply the system with power, the accuracy and processing speed of the system are effectively guaranteed. Meanwhile, these methods solve the problem of camera wire winding fundamentally. Experiments show that the system measures light leak degree accurately and has a good repeatability, and meets the requirements of relevant standards and engineering application.