In the domain of digital communication, the base band signal is usually regarded as the code's one kind of electricity expression. But in the actual base band transmission system, not all base bands electricity wave can transmit in the channel, therefore choosing the code that adapts to carry on the the base band transmission system is very important. The HDB3 code is one of a representative codes, it maintains the AMI's merits and also overcomes its shortcoming simultaneously. This article performs the ASIC design to the HDB3 encoder. This HDB3 encoder chip has the merit of stable performance, quick speed, low cost, good timeliness, and so on.