A fuel reforming system may include an engine combusting reformed gas to generate mechanical power; an intake line connected to the engine to supply reformed gas and air to the engine; an exhaust line connected to the engine to circulate exhaust gas exhausted from the engine; a fuel reformer provided at an exhaust gas recirculation (EGR) line diverging from the exhaust line, mixing the EGR gas passing through the EGR line with the fuel and reforming the fuel mixed in the EGR gas; and an EGR flow controller determining a target opening degree of a flow rate control valve according to engine running condition, whether or not in a reforming running condition, required amount of EGR gas along to running condition, and controlling opening degree of the flow rate control valve on a basis of the target opening degree.