The invention discloses a dynamic calculation method for the gravity center position of a tunnel trackless self-propelled variable-mass platform vehicle. The device mainly comprises establishing a coordinate system I, and obtaining the offset of the gravity center G of the platform vehicle under the coordinate system I, establishing a moment balance equation, obtaining an initial position coordinate of the gravity center G of the platform truck under the coordinate system I, and establishing a coordinate system II; acquiring position coordinates (x ', x'') of the gravity center G of the platform truck under the coordinate system II; y '', z'') of the platform car and obtaining the barycentric coordinate of the barycentric G of the platform car after the posture is changed; obtaining the offset of the gravity center G of the platform car relative to the central axis of the platform car through a moment balance equation, obtaining the height of the gravity center through three-dimensional software modeling simulation and calculation, and obtaining the coordinate of the gravity center G of the platform car relative to the center of the tunnel; and finally, obtaining the barycentric coordinates of the platform car by the spatial three-dimensional coordinate conversion matrix after the posture changes, real-time monitoring of the barycentric of the platform car is realized, the accuracy is high, and the cost is low.