An exhaust system, may include an exhaust line through which exhaust gas passes, a nitrogen oxide purification catalyst that is mounted on the exhaust line to reduce nitrogen oxide of the exhaust gas, an injector that is mounted at an upstream side of the nitrogen oxide purification catalyst to additionally inject fuel such that nitrogen oxide that is trapped in the nitrogen oxide purification catalyst is detached to be reduced thereby, and a control portion that varies an injection pattern of the injector if it is determined that a purification rate of the nitrogen oxide purification catalyst is higher than a first predetermined value.