In Cognitive Radio Networks (CRNs), when the Primary Users (PUs) appear, the SUs have to evacuate the licensed spectrum in use or reduce the transmit power so that no harmful interference is introduced to the PUs. In this paper, we explore the multiple Secondary Users (SUs) coexistence system in CRNs based on power control mechanism and interference temperature model. We propose an optimal solution that can maximize the channel capacity and minimize the spectrum handover overhead, constrained by the accumulated interference of both the SUs-to-PU and SUs-to-SUs. We formulate this problem as a non-linear optimization problem and propose a heuristic algorithm to solve it efficiently. Experimental results show that compared with two alternative approaches, our algorithm can improve the usage of the spectrum by up to 51% (with a random approach) and up to 278% (with a conservative approach).