A Chip-less Radio Frequency Identification (CRFID) metal crack sensor with a single resonant structure is proposed to simultaneously detect crack width and direction. The circular and the rectangle with tangent corners resonators are integrated into the design, and the electromagnetic simulation software HFSS is utilized to optimize the structure and simulate the performance of the sensor. The response characteristics of Radar Cross Section (RCS) of the sensor under different defect cracks are studied systematically. It is found that frequency shift is proportional to the crack width. The results show that the crack direction and crack width on the metal structure can be identified by the change of the resonant frequency of the sensor. The frequency shift direction in RCS amplitude-frequency characteristics in the two polarization directions correspond to the direction of the crack, and the resonant frequency shift is proportional to the crack width. The CRFID sensor can detect cracks in submillimeter width in three directions: 0°(horizontal), 90°(vertical), 45° or 135°(oblique), among which the crack detection sensitivity can reach up to 43.5 MHz/0.1 mm.