The invention discloses a porous medium combustor for a low-caloric-value gas fuel. The porous medium combustor comprises an oxygen-enriched conduit, an ignition air gun, a premixed combustion chamber, secondary air pipes and a combustor nozzle of which the central axes are coincident; the secondary air pipes are coaxially sleeved outside the premixed combustion chamber; air pipelines and fuel pipelines which circumferentially incline are correspondingly arranged on respective pipe walls of the secondary air pipes and the premixed combustion chamber; a mixing chamber, a mixed fuel gas uniformdistributor, a small porous medium and a large porous medium are sequentially arranged in the premixed combustion chamber along an airflow direction; air holes of the small porous medium and the large porous medium adopt a honeycomb arrangement structure; the oxygen-enriched conduit is coaxially sleeved outside the ignition air gun; and outlet ends of the oxygen-enriched conduit and the ignition air gun pass through a wall surface of the premixed combustion chamber and extend into the mixing chamber. By adopting the segmental type porous medium, the combustion stability of the low-caloric-value gas fuel can be obviously improved, the combustion intensity of the low-caloric-value gas fuel is enhanced, the combustion volume is reduced, the combustion efficiency is improved, and the discharge of pollutant can be effectively reduced.