The invention provides a conveyor rubber belt longitudinal tearing detecting system based on ultrasonic waves. The conveyor rubber belt longitudinal tearing detecting system comprises an ultrasonic signal generating device and an ultrasonic signal receiving device which are arranged at the two ends of a conveyor rubber belt respectively and an ultrasonic signal analyzing device connected with the ultrasonic signal receiving device. A conveyor rubber belt longitudinal tearing failure detecting method of the system comprises the steps that the ultrasonic signal generating device continuously sends ultrasonic signals on one side of the conveyor rubber belt; the ultrasonic signal receiving device receives the ultrasonic signal in real time and sends the signals to the ultrasonic signal analyzing device after the ultrasonic signals are processed; the ultrasonic signal analyzing device processes received detecting signals in real time, the detecting signals are compared with a built-in failure judgment threshold value to judge whether a failure occurs or not, and when the failure occurs, sound-light alarming is carried out locally. The system is simple in structure, low in cost, capable of greatly improving the failure detection rate, good in real-time performance and detection effect, high in work reliability, suitable for dust, water spraying and other complex work conditions, and high in applicability.