Without the priori information of interference system, iterative detection algorithm can make a good performance. However, most of current iterative energy detection algorithms are confined to the hypothesis that the SNR within the entire detecting band is the same, which is obviously unrealistic in realistic application, especially when the frequency band is quite wide. Aiming at such a problem, this paper presents a wideband sampling model with different SNRs in various frequency bands, and then it proposes an improved wideband energy detection algorithm based on the frequency correlation of the authorized signals. The simulation results show that when there are a variety of signals with different power in the detection band, the proposed algorithm still has a good detection performance.