In this paper, we address the problem of bandwidth sharing among multiple primary users and multiple secondary users in a cognitive radio network. In cognitive radio networks, effective spectrum assignment for primary and secondary users is a challenge due to the available broad range of radio frequency spectrum as well as the requisition of harmonious coexistence of both users. To handle this problem, firstly, Bertrand game model is used to analyze a spectrum pricing in which multiple primary users emulate with each other to acquire maximal profit. After that, we employ Cournot game to model the spectrum sharing of secondary users to obtain optimal profit for each user also. Simulation results show that our scheme obtains optimal solution at Nash equilibrium.