UHF passive RFID has been already in practice. Industrial applications sometimes suffer insufficient tag readability. Engineering may be needed to enhance the readability, accordingly. One of the factor to deteriorate the readability is the multipath fading. Identification of principal reflecting paths is essential to improve the readability deterioration by, for example, using antenna diversity and usage of microwave absorbance materials to suppress reflections. In this paper, a path identification method for UHF RFID using the measured power profile is presented. The method only requires a series of the received power measurement at the position of the target tag. By applying the steepest gradient method, we can optimize the parameters that defines the reflecting plane and eventually identifies the path direction. Together with theoretical development of the method, numerical example shows the validity of the method.