The concept of centralized filling and separate bottle displacement was introduced to reduce the inconvenience of filling compressed natural gas(CNG) vehicles. By taking a programmable logic controller (PLC) as the smart control unit and stepper motors as drive units, a mobile threedimensional table was designed as a working platform. The stepper motor control algorithm was studied, and the system model for the CNG vehicles automatic loading and unloading was constructed. A new automatic loading and unloading system for CNG vehicle bottles was developed. Theoretical analysis and experimental results show that the system can complete the automatic loading and unloading task in 1 or 2 minutes, thereby improving CNG vehicle filling efficiency.