The utility model provides a vehicle license plate frame sensor belonging to the field of alarm devices, which comprises a vehicle license plate frame shell, a plate frame bottom case and a sensing assembly. The vehicle license plate frame shell is the frame-structure with sensing assembly-mounting holes in the center of the upper or the bottom edge. The plate frame bottom case serves to fix the sensing assembly on the vehicle license plate frame shell. Four fixation mount holes are equipped on the vehicle license plate frame shell in correspondence to the mount positions of the car license plate. The sensing assembly comprises a cylindrical shell, a circuit board, a cover arranged at the lateral side of the cylinder, and a sensor. The utility model has the advantages of simple structure, reasonable design, easy installation, and convenient use.