The invention belongs to the technical field of fracturing equipment of oil and gas wells and relates to an online monitoring system for a fracturing pump truck fluid end. The online monitoring system comprises an optical fiber sensor and a sensor power source which are arranged at the fracturing pump truck fluid end. The optical fiber sensor is in electric connection with a data preprocessing device. The data preprocessing device is in electric connection with an optical fiber sensing instrument. The sensor power source, the data preprocessing device and the optical fiber sensing instrument are all connected with a system power source. The system of state detection and failure analysis and prediction for the fracturing pump truck fluid end is established, so prejudgment on the working conditions of the fracturing pump truck fluid end is achieved. According to the online monitoring system, the situation that in the fracturing construction process, construction fails due to a equipment failure is effectively reduced, and the risk that in the fracturing construction process, staff enter a high-pressure area to monitor the operation conditions of the fluid end, as a result, the staff are injured due to high-pressure pipeline bursting is avoided; meanwhile, the maintenance time of the fluid end is shortened, partial elements in a good state are prevented from being maintained excessively, in this way, the service life of the equipment is prolonged, the production cost is lowered, and operation efficiency is improved.