Abstract: Based on nonparametric CUSUM algorithm, an UWB signal quickest detection algorithm is proposed, to solve the problem of UWB signal detection in CUWB (cognitive UWB) system. According to the low duty ratio property of UWB signal, short time energy is selected as the observation statistic to connect the block detection idea and the sequence detection idea, which conquers the SNR wall problem. A slipped pretreatment window is adopted to depress the noise interference to observation statistic. To more decrease the detection delay, the Reference Value of CUSUM algorithm is adaptively changed in improved algorithm. It is improved by simulation that the proposed algorithm can achieve more than 90% detection probability, under the condition that duty ratio is 1/6 and SNR= -25dB, within 50 transmitted pulses, and energy detection algorithm can achieve the same detection probability when SNR=8dB. Under the condition SNR -10dB, the improved algorithm can obviously decrease the detection delay.