The invention discloses a system and a method for locating an inspection robot in a petrochemical plant. The system comprises a global positioning system (GPS) observation unit, an ultra-wide bandwidth (UWB) observation unit, a visual observation unit, a laser observation unit, a mileage observation unit, a combination decision module, an inertial state estimation module, an available positioningobservation/strapdown inertial navigation system (SINS) combination module, and a positioning information fusion module. The GPS observation unit, the UWB observation unit, the visual observation unit, the laser observation unit and the mileage observation unit acquire the respective observation data and send same to the combination decision module; the combination decision module performs multi-layer map-based positioning by combining an environmental map model stored in an environmental model prior information module so as to determine available observation types; the available positioning observation/SINS combination module combines available observation data with a corresponding motion equation established by an inertial state estimation module, and the combined result is sent to the positioning information fusion module for carrying out final integrated pose estimation. The system and the method solve the problem of seamless positioning of the inspection robot which runs in various complicated regions of the petrochemical plant, and guarantee the continuity of a positioning process and the stability of the positioning result.