In cognitive radio networks, when primary users (PUs) do not use a shared frequency band, secondary users (SUs) are allowed to use that frequency band. However, when SU using frequency band and reclaiming PU also wants to use this band, there are two solutions: SU jumps to another existing spectrum band or stays in the same frequency band and changes its power so that interference in the reclaiming PUs does not exceed a threshold. Since the first solution interrupts the SUs' work, the second solution is more appropriate. Therefore, power control in cognitive networks is absolutely significant which should receive more attention. In the previous work (TPC-CBS) [2], TPC algorithm has been used for power control. The drawback of this algorithm is fixed target SIRs. In other words, while using this algorithm, all the users having enough sources or extra sources reach the same target SIR, which is not desirable. Therefore, in this paper, we are going to solve it by means of the proposed algorithm called "An Efficient Distributed Power Control Algorithm for Cognitive Networks (EDPC)". By the proposed algorithm, when a user has a bad channel, its SIR sets to the minimum target SIR and, when it has a good channel, its SIR will be more than the minimum value. Moreover, by means of fuzzy logic systems (FLS), the value of interference on reclaiming PU caused by SUs is checked in each iteration and power level of SUs is decreased if this value exceeds a threshold. Simulation results show that using our proposed algorithm not only allows SUs and PUs use frequency band simultaneously, but also enhances throughput significantly in comparison with the previous approaches (TPC-CBS).