An apparatus for alerting a parking floor includes an electronic control unit configured to: determine an entrance of a parking lot; measure a slope of a vehicle; perform wireless communication with an external device through a wireless communication network; determine a current location of the vehicle; determine a gear stage of the vehicle; and compare the slope of the vehicle with a first setup value corresponding to an underground parking lot or a second setup value corresponding to a ground parking lot when the vehicle enters the entrance of the parking lot to determine movement of the vehicle to each floor and determine a parking floor value corresponding to a floor at which the vehicle reaches.