A system and method are provided for clocking the speed of a moving object using a wireless terminal in a preview mode of a camera, wherein the method includes the steps of entering a preview mode for speed measurement when a speed measurement function is selected in a camera preview mode of the wireless terminal, measuring a moving distance of an object in the preview mode for speed measurement, measuring a moving time period of the object in the preview mode for speed measurement, and measuring and displaying a moving speed of the object by using the moving distance and moving time period of the object which have been measured. The method can further include steps of measuring a moving time period of the object by receiving image data of a moving object through two camera units in the preview mode for speed measurement, measuring a moving distance of the object through the two camera units in the preview mode for speed measurement, and measuring and displaying a moving speed of the object by using the moving distance and moving time period of the object which have been measured.