Train integrity monitoring method based on GNSS

The invention provides a GNSS (Global Navigation Satellite System)-based train integrity monitoring method. The method comprises the following steps: eliminating a clock difference between receivers of a satellite and a train and an error between a troposphere and an ionosphere by adopting a double-difference carrier phase to obtain an observation equation of the double-difference carrier phase of Kalman filtering; according to the observation equation of the double-difference carrier phase, the relative position between the two antennas of the train is dynamically estimated through a Kalman filtering algorithm, and the train length is calculated according to the relative position between the two antennas; a difference value between the train length obtained through calculation and a given reference train length is obtained, and if the difference value is within a given threshold range, it is considered that the integrity state of the train is normal; on the contrary, if the difference value exceeds the thres