The invention discloses a train approach alarming trigger device. The device adopts an orthogonal Doppler radar detection technique, under the circumstance that detection equipment does not need to be mounted on an upper track, for example, the device can be mounted outside a train track guard railing and within the range of 30 meters away from a train track, both train approach detection and train approach direction detection can be realized, and trigger signals are provided for a train approach alarming device. The device comprises a radar sensor module, a Doppler signal amplification conditioning module, a power management module, a dual-backup physical isolation wireless receiving and dispatching module (a radio frequency processing module 1 and a radio frequency processing module 2), an MCU module, a minimum system, a serial communication module, an outside watchdog module and the like. The device has the outstanding characteristics that the Doppler radar detection technique is adopted, the device has a low power consumption control mode, the dual-backup physical isolation wireless receiving and dispatching module is used for reliably uploading detection information, a solar electricity supplying scheme can be supported, reliable stable trigger signals are provided for train approach alarming, and besides, the device is convenient to mount and high in applicability.