Abstract: The application of magnetic flux leakage(MFL) technique on atmospheric tank was introduced, and its main influencing factors were analysed. A storage tank which is about 0.1 million m3 in volume was inspected by FloormapVS2i, after which the overall diagram of the tank bottom by MFL was obtained and presented, then the defects were analyzed and rechecked by ultrasonic thickness gauge. It suggests the magnetic flux leakage technique together with other nondestructive technique, such as ultrasonic testing, penetrate testing, can evaluate the condition of tank bottom accurately and efficiently, which ensures its safe operation.