Abstract: Because the outside factors and instruments and/or devices disturb these methods, the reliability of measured results got from conventional methods is low. The various inspection methods on how to inspect the bottom leakage of tank at home and abroad are introduced. The indirect inspection method is to inspect whether the oil film is floating on the water or not in the drainage ditch of the tank, which is called oil film inspection method. The paper introduces the fundamentals and characteristics of the indirect inspection methods covering relative density difference inspection, high-frequency current inspection, light reflection ratio inspection, resistance inspection and electrostatic capacity inspection. The direct inspection method is to directly contact with leaked liquid with sensors to inspect its variation in physical and chemical behaviors. What more the paper introduces are the conductive powder element inspection method, cable inspection method and optical fiber inspection method.