This paper presents a group persistent assignment method in contention slots for DOCSIS standard. Our model is a numerical method which can separate each user access to the arbitrary contention slot with independent persistent value. Each user can be collected into a group access. Then we can assign different persistent value to access slots in a frame. The occasion that many users access in same slot is reduced. In this paper, we also calculate the value of successful probability and average successful number in each contention period.