Abstract: According to the actual spectrum demand of cognitive radio, a new spectrum-hole detection algorithm, which bases on triple matrix accumulation, is presented for?cognitive?radio?systems?for?the?first?time by the study on weak signal detection technology. The algorithm combines spectrum-domain block adaptive filtering with matrix reshape, accumulate products estimation and frequency-domain smoothing to realize the weak signal detection. Finally, the performance of the algorithm is analyzed and?simulated?by?using?a?QPSK?signal. The result shows that the detection technology can detect weak signal quickly and effectively, and has a higher detection probability. The detection technology may be applied wholly to cognitive radio field.