A method and system for controlling a wheel slip of a vehicle without using a reference speed is provided. The system includes a speed detector that detects a speed of a driving device for operating the vehicle and a controller that determines a torque calibration command based on a torque command of the driving device, and a current speed and a past speed of the driving device detected by the speed detector. The torque command of the driving device is calibrated using the determined torque calibration command, and a driving device is operated based on the calibrated torque command.