The present application discloses an apparatus and a method for pipeline corrosion online inspection, ultrasonic guided wave is used for pipeline inspection, about 30 meters of inspection check requirements of a thermal insulation layer pipeline can b met only by removal of 1/30 of thermal insulation and building of 1/30 of scaffolds, so that 29/30 of cost can be saved (ultrasonic guided wave long distance inspection fee and ordinary inspection fee overruning part is not deducted), in addition, if a thermal insulation material is removed, waste thermal insulation material solid waste disposal is increased, and energy conservation and emission reduction and environmental protection burdens of enterprises in the prior art can be increased. When in trenchless inspection of a buried pipeline, a manner of use of trenchless inspection anticorrosive coating inspection for deduction of possible corrosion situations of the buried pipeline is changed into a possible manner of direct inspection of the corrosion situations of the buried pipeline, and the correct probability of judgment in good situations of the pipeline can be improved.