A method of improving fuel efficiency by analyzing a driving pattern of a vehicle may include: calculating weighting factors according to a driving pattern of the vehicle at coordinates, which are the ratios of weightings accumulated at the coordinates to the sum of the weightings accumulated at all coordinates in an engine operation region; calculating a reference fuel consumption ratio KFUEL and a reference NOx exhaust ratio KNOx using the weighting factors; determining whether the reference NOx exhaust ratio KNOx exceeds a predetermined comparative value; and controlling an engine to improve fuel efficiency when the reference NOx exhaust ratio KNOx is equal to or less than the predetermined comparative value.