A low power,portable,cheap and high precision detection system is developed to measure the concentration field of powder steam,and it is suitable to requirement of laser robot repair. The system mainly consists of 532 nm,100 mW semiconductor laser,sheet of lens,charge coupled device (CCD) camera and analysis software. It is shown that the consistency in the detection of volume of concentration distribution of metal powder stream and the theoretical calculation is very good. The system could be an effective guiding significance for the design of co-axial nozzle and the determination of powder stream parameter in robot laser repair.