A method of estimating road slope using a gravitational acceleration sensor, includes determining whether a driving mode of a vehicle is a towing or freight carrying mode, calculating a difference value between road slope measured using the gravitational acceleration sensor and road slope measured using a driving torque when the driving mode of the vehicle is the towing or freight carrying mode, estimating road slope by correcting the road slope measured using the gravitational acceleration sensor based on the difference value, and controlling a shift of the vehicle according to the estimated road slope.