Photoelectric detecting technology has been adopted to check to see if there are faults, knots etc. in the threads on the warping machine. Then, the signal to show the evidence of faults is not obvious but weak at the terminal because of the threads' rapid movement, vibration and of the strong light and electric interference in the site. In order to strengthen the sensitivity of weak signal in detection, measures such as dynamic detection, reduction of circuit noise, dual judgment, etc. are employed, thus the system's false ratio in detection is greatly decreased while its reliability is improved.