We assume that mobile users only establish direct link( with users in the same eNodeB. We set a parameter about maximum tolerance distance between D2D pair. Therefore 020 pairs will become cellular users to ensure their performance when the distance between them is longer than maximum tolerance distance. Cellular users are randomly distributed in the area of eNodeB firstly. Then we randomly select some cellular users to be 020 users according to a certain proportion. The selected 020 users find out a user who satisfies the condition of matching direct link, and can make up D2D pair.