The invention discloses an intelligent filling method for an underground cavity. The method includes the following steps of filling preparation; scanning of inner chamber of the underground cavity; modeling of filling data; 3D printing filling, and the like. After a detection robot unit completes the scanning of the underground cavity, a three-dimensional model of the underground cavity is constructed; a central control computer of a centralized electric control unit performs applying stress field calculation analysis on the outside of the three-dimensional model; support models are sequentially constructed on stress concentration point positions of the inner surface of the three-dimensional model to generate spatial three-dimensional support models, and 3D printing paths and print reference coordinates are generated based on the three-dimensional model of the underground cavity and according to an applying stress field calculation analysis result and an input safety factor; and a 3D printing robot unit 3D prints a spatial three-dimensional support entity inside the underground cavity. According to the method, controllable support quality and controllable filling amount can be achieved; high filling efficiency and high safety can be achieved; space reuse can be achieved; and the method is especially suitable for filling and treatment operation of the underground cavities.