The invention discloses a railway train triggering system applied to a bridge real-time online monitoring system. The railway train trigger system comprises a trigger controller and at least two groups of trigger assemblies; the two groups of trigger assemblies are arranged on the same side of the railway, and the trigger assemblies are separated from the railway by a first preset distance; the two groups of trigger assemblies are separated by a second preset distance; the trigger controller is installed below or on the side surface of the bridge; each group of trigger assemblies comprises a vertical rod support, a laser trigger sensor and a power signal box; a laser trigger sensor is arranged at the top of the vertical rod support, and the power signal box is arranged in the middle of thevertical rod support; the laser trigger sensor on the upright rod support is connected with the power supply signal box through a switch signal wire; the trigger controllers are connected with the power signal boxes in the two groups of trigger assemblies through optical fiber signal lines respectively. The system realizes non-contact detection by using a laser trigger sensor, and realizes accurate identification, high-speed long-distance triggering and high-speed long-distance transmission of parallel vehicles; and the system is simple in structure and convenient to install.