Abstract: In this paper, a chipless RFID sensor based on frequency domain is designed by using metal strips as resonators.When the crack on metal surface is detected, resonant frequencies of the resonators will change, and the location and direction of the metal crack can be detected by analyzing the frequency changes with RFID technology.By dividing different detection areas in the sensor coverage and setting the number and layout of metal strips reasonably, the crack location can be detected.In addition, by placing the metal strip horizontally and vertically, the horizontal and vertical polarized plane waves can be scattered respectively, and the crack direction（horizontal or vertical） can also be detected.For this purpose, four horizontal and four vertical metal stripe resonators were designed in the operating band of 8 GHz～11.5 GHz. the location and direction of cracks on the metal surface are identified by building and simulating the sensor model, and distinguishing the eight resonant frequencies generated by the excitation of two polarization modes.Finally, the actual sensor label is made and measured, and the measurement and simulation results are in good agreement, which verifies the feasibility and practicability of the designed sensor.