The present invention relates to method for filling deformable karst cave, and the steps are: penetrating a grouting pipe into an elastic silicone tube, penetrating the grouting pipe and the elastic silicone tube into a deformable bracket, and lowering into a karst cave; sealing the elastic silicone tube, injecting silicate resin materials into the grouting pipe, and injecting steel fiber reinforced grout to implement a “block stone-like” structure; sealing the elastic silicone tube, separating the “block stone-like” structure from the elastic silicone tube to complete a “block stone-like” structure; lowering the elastic silicone tube and the deformable bracket, sealing the elastic silicone tube, lowering the elastic silicone tube and the deformable bracket tore construct the “block stone-like” structure, and completing the filling. The present invention may effectively stabilize the karst cave, ensure safe tunnel construction and stable surrounding rocks, and improve engineering construction speed.