Abstract: In order to realize real-time, high efficiency and high precision measurement of wall thickness of a polyethylene terephthalate (PET) bottle, through theoretical simulation and experimental verification, taking a PET bottle in 3.5mm thick as an example, the optical model for measuring the wall thickness of the PET bottle was set up. According to the principle of ray tracing, the feasibility of applying reflective fiber optic displacement sensor to measure the wall thickness of a PET bottle was proved. The simulation was carried out by LIGHTTOOLS software. Finally, a device based on reflective optical fiber displacement sensor to measure the wall thickness of PET bottle was designed and verified by experiment. The results show that, the measurement range is 3.20mm~3.80mm, the linearity is 15.8% and the sensitivity is 0.8448mV/μm. Compared with the traditional measurement method, the measurement efficiency of the experimental device will be increased more than 30%. The study has reference value for improving the efficiency and accuracy of actual detection.