A bottom beam for a roadway hydraulic support high in energy absorption speed, burnt resistant and floor heave resistant is characterized in that a plurality of burst energy absorption unit mounting cavities are evenly distributed in a counter-arch variable section box beam, burst energy absorption units are located in the burst energy absorption unit mounting cavities, carbon fiber cloth is located below the burst energy absorption units and is tightly attached to the bottoms of the burst energy absorption units, the end of the carbon fiber cloth is fixedly connected to the counter-arch variable section box beam, each burst energy absorption unit comprises an energy absorption block and a burst block, with the energy absorption block being located above a top board of the burst block and the top of the energy absorption block being tightly attached to the upper wall of the corresponding burst energy absorption unit mounting cavity; the sidewall of each burst energy absorption unit mounting cavity is provided with guide ribs, and side boards of the burst blocks are provided with guide grooves; the guide ribs are located in the guide grooves; the burst blocks are in sliding fit with the sidewalls of the burst energy absorption unit mounting cavities; the energy absorption blocks are made of metal thin-walled tubes filled with porous foam alloy material; the upper and lower end faces of each energy absorption block are planes parallel to each other; the upper end face of the top board of each burst block is planar; the lower end face of the bottom board of each burst block is arced.