Catalyst effect improvementing device and method

Disclosed are a device for improving the catalyst efficiency of a vehicle and a method thereof. The device for improving the catalyst efficiency of a vehicle comprises an oxidation catalyst installed in an exhaust gas pipe of an engine for reducing pollutant emissions contained in the exhaust gas, a modifier installed in the exhaust gas pipe in the state of contacting with the oxidation catalyst and partially oxidizing fuel and an oxidizing agent to produce modified gas, a fuel sprayer spraying fuel installed in the exhaust gas in the front of the modifier, and an air flow path supplying air from the interval between the fuel sprayer and the modifier to the inside of the exhaust gas pipe.