To solve the target detection problem caused by the low signal-to-noise ratio (SNR) of the laser active imaging system, a multichannel sequential detection algorithm is presented. Based on the original observed data, the calculation for judging threshold of laser active imaging system is proposed according to the generalized log-likelihood ratio. The multichannel characteristics of laser active imaging system are considered and the sequential probability ratio test (SPRT) is implemented to detect the targets in intensity image channel and range image channel, while controlling the rates of false alarms and missed detections. Theoretical analysis and experimental results show that the performance of the multichannel sequential detection algorithm is excellent. The results allow us to conclude that the use of the sequential detection algorithm substantially reduces the required time and the sample size of the system. This new target detection method satisfies the accuracy and real time requirements for laser active imaging guidance.