In wireless networks, implementing repeaters can improve network capacity and CCTSS systems can be used to mitigate interference. This paper discussed the selection of covering shapes in a given area, and presented an optimum scheme of channel assignment and PL allocation. Meanwhile, the 3-colour theorem and 4-colour theorem in graph theory will be given. At last, we introduce the application of 3-colour theorem and 4-colour theorem in the problem of repeaters’ site selection. By the relevant calculation, we can prove the application is reasonable.