Abstract: In order to overcome the difficulties in detecting the longitudinal corner cracks of containers, such as motor vehicle oil tanks, are difficult to detect, a multifunctional system used to detect magnetic flux leakages of tanks is designed and developed based on differential hall probes. The detection probe is made of two elements forming the structure of differential type, make up the detection probe, which can improve the sensitivity of detection system. By switching different pole shoes, cracks of the plane and the corners can be detected respectively. As an external trigger, the photoelectric encoder can collect data at the same distance each time, to determine where the defect exists accurately. Through carrying experiments on the fuel tank belonging to a heavy armored vehicle with prefabricated defects, acquired results show that the detection system can identify the the longitudinal cracks inside the tank, then it can be promoted to industrial applications.