The invention provides an underwater pipeline detection device based on a fiber laser. The underwater pipeline detection device comprises a body and a control system, flanges are symmetrically arranged on the two sides of the body, and through holes are formed in the flanges. A storage box is fixedly installed at the bottom of the body, a fiber optic receiver and a fiber optic emitter are symmetrically installed on the two sides of the top of the storage box, a fiber optic sensor is fixedly installed on one side of the fiber optic receiver, and a fiber optic is fixedly installed between the fiber optic emitter and the fiber optic receiver. According to the underwater pipeline detection device based on the fiber laser, the service life of a small engine is prolonged, data detected for multiple times are compared, whether oil and gas leakage happening to a certain segment of a pipeline or not can be determined, the operation is simple and convenient, the positioning is accurate, and through the fiber optic sensor outside the body, the situation that the pipeline is damaged due to reduced soil on the periphery of the pipeline and the environment is polluted due to the oil and gas leakage is prevented.