In view of the fact that the current monitoring technology of track occupancy detection is easy to be influenced by electromagnetic interference and external environment, and it is difficult to realize large capacity and high density measurement, a new method based on strain sensing of weak fiber grating array is proposed. Firstly, the weak fiber grating array with reflectivity of 0.2‰ and the hybrid multiplexing technology are used to solve the problem of large capacity and high density detection. Secondly, based on the finite element model and wheelrail coupling theory, this paper deduces and analyzes the force on the track and the sensitivity of the sensor. Finally, the packaged fiber grating array is installed on the test site, and the track load experiment is carried out. The experimental results show that the system can accurately identify the axle information, running direction and track occupation information. The system has good reliability and high sensitivity, which provides a new idea for track occupation inspection technology.