Provided is a system for supplying a reformed product from by-product gas to a catalyst regenerator of a catalytic olefins production process. The system includes a reactor configured to mix naphtha and a catalyst to produce olefins through a cracking reaction of naphtha, and then separate the coked catalyst and olefins to discharge the coked catalyst, a catalyst regenerator configured to regenerate the coked catalyst introduced from the reactor and recirculate and supply the regenerated catalyst to the reactor, an air supplier configured to supply burning air to the catalyst regenerator, and a catalytic partial oxidation reformer configured to reform by-product gas containing methane as a main component to supply a reformed product containing hydrogen and carbon monoxide as a main component to the catalyst regenerator and regenerate the coked catalyst.