Method for predicting NOx amount and exhaust system using the same

A method for predicting a NOx amount may include detecting an 02 amount in an intake air, calculating a reference 02 amount in the intake air according to a driving condition of an engine, calculating a reference NOx amount contained in an exhaust gas according to the driving condition of the engine, and primarily correcting the reference NOx amount based on the detected 02 amount in the intake air and the reference 02 amount in the intake air according to the driving condition of the engine.