Abstract: Based on the analysis of modulation codes for optical disc, a 3/8 code rate RLL（4, 11） code is presented, whose density ratio is 9 4% higher than that of EFM The encoder of this code is designed A novel tentative algorithm is used in design of the encoder, which makes the number of encoder states reduce to 14, greatly simplifying the encoding and decoding process After that, the decoder of this code is discussed, and the window length of the sliding block decoder as well as the anticipation of FSTD（finite state transition diagram） are estimated Because this code is not a dc free modulation code, systems that use it must have some dc control measures Therefore, the situation that is more suitable to this code is characterized