In this paper, a new converter for plastic optical is proposed .The whole system is divided into 5 parts and each of them are introduced. In this experimental system, the M array is used to replace the actually data sources. Then change the M array into the CMI code. Through the optical-electric transmission part, the signals are sent to the CMI decode part in which the original M array is recovered. The circuit board by which the data signals can be transmitted has been achieved in lab. The parameters of the system are discussed. The relationship between the system clock and BER(bit error rate) is analyzed. Several different factors which have effects on the system's performance are discussed. In order to patch with RJ-45, the further work mainly focus on the connection with the nowadays netcards which are widely used in PC and LAN.