Forward error correction is the key technology to ensure the reliability of data transmission in 25 G-EPON system. For 25 G-EPON system, random errors and continuous burst errors often occur in the process of data transmission due to the high transmission. By analyzing the RS coding and decoding algorithm and selecting the appropriate RS characteristic parameters, the influence of these parameters on the transmission performance of 25 G-EPON system is simulated and analyzed. Then the appropriate RS code scheme is chosen for 25 G-EPON communication system. The experimental results show that under the premise of satisfying the reliability of the 25 G-EPON system, the coding efficiency should be reduced as much as possible, the redundancy of coding should be improved and the coding scheme with shorter code length should be adopted, so as to improve the coding gain of the RS code and reduce the bit error rate of information transmission. It is shown that RS (1023, 847) code can correct up to 880 bits errors consecutively, and the coding gain can reach 8.834 dB when the symbol error rate reaches 10－12, which can meet the transmission requirements of 25 G-EPON system. Therefore, RS(1023, 847) code is selected as the forward error correction code of 25 G-EPON system.