The present invention provides a method of identifying noncompliant fuel of a vehicle and improving drivability. The method comprises: (a) confirming a present coolant temperature after the vehicle has been started, (b) setting a coolant temperature factor value based on the coolant temperature, (c) setting an RPM reference value based on the RPM, (d) determining whether an RPM incremental value reaches the RPM reference value, (e) setting a calibration learning value if the RPM incremental value is smaller than the RPM reference value, (f) calculating a learning value of fuel injection volume, (g) calculating the fuel injection volume for start injection based on the calculated fuel injection volume, (h) determining whether a start state of the vehicle has completed, and (i) calculating the fuel injection volume after start injection and fuel injection for acceleration or deceleration if the start state has been completed.