A method of controlling the engine of a hybrid electric vehicle is provided to effectively reduce nitrogen oxides(NOx) discharged after releasing idle stop due to overcharged oxygen to catalyst at the time of fuel-cut and idle-stop. A method of controlling the engine of a hybrid electric vehicle includes a step(ST120) of deciding whether fuel is cut off while the vehicle is running, a step(ST130) of calculating amount of overcharged oxygen in catalyst if fuel is cut off, a step(ST160) of activating fuel injection control to reduce nitrogen oxides(NOx) caused by overcharged oxygen in a three way catalyst under excessive lean condition after fuel cut or idle stop when calculated overcharged oxygen is greater than a reference value, a step(ST180) of calculating amount of fuel to be injected from the calculated amount of overcharged oxygen when idle stop signal is emitted from the HCU(Hybrid Control Unit), and a step(ST200) of removing oxygen overcharged in the three way catalyst by injecting the calculated amount of fuel when engine rpm is less than a prescribed value.
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