A safe early warning method and device for full-section tunneling of a tunnel featuring dynamic water and weak surrounding rock, comprising establishing a dynamic coordinate system with an origin thereof moving along a tunnel excavation line, recording the moving distance of the origin, conducting three-dimensional laser scanning with the origin as a center to obtain point cloud data including coordinate data, collecting surrounding rock data; conducting deformation fitting on the point cloud data, calculating a fitting residual error, removing a noisy point, and conducting preprocessing; combining data of preprocessed point cloud, surrounding rock, and the tunnel excavation line to construct a tunnel excavation dynamic model; conducting stress analysis according to the model and determining whether to send out a safety early warning signal. The device comprises a three-dimensional laser scanner, a geological radar device, a displacement module, an industrial computer, a data transmission module, an alarm, and a server.