The invention discloses a method for determining
oxygen concentration of
exhaust gas of an engine. The method comprises the steps that firstly, the inflation efficiency of the engine, the rotating speed of the engine and the exhaust amount of the engine are utilized for calculating the total gas inlet
mass flow of the engine, and then, the temperature of air entering the engine, temperature of the
waste gas entering the engine, temperature of
mixed gas entering the engine and the total air inlet
mass flow of the engine are utilized for calculating the
mass flow of air entering the engine and the mass flow of the
waste gas entering the engine; on the basis of data, the
oxygen concentration of the
waste gas of the engine can be determined. According to the method for determining the
oxygen concentration of the waste gas of the engine, after the engine is started, the oxygen concentration of the waste gas in the engine can be rapidly determined, sensibility of a pipeline structure is reduced, so that the requirement of pipeline
layout of the engine can be reduced. The invention further discloses a
system for determining the oxygen concentration of the
exhaust gas of the engine.