The invention discloses a gas-liquid pressure cylinder. The gas-liquid pressure cylinder is not provided with an oil storage cavity and is simple and compact in structure, convenient to maintain, high in efficiency, and saves energy. An oil inlet is formed in a liquid cylinder body and communicated with an oil storage tank of a braking system through a one-way valve. When the pressure cylinder does not have pressure air, the one-way valve is opened, and the oil storage tank is communicated with the pressure cylinder. After the pressure cylinder is filled with compressed air, due to the pressure action, the one-way valve is closed, and the passage between the oil storage tank and the pressure cylinder is cut off. The gas-liquid pressure cylinder can realize automatic oil supplement, lowers the labor intensity, and is low in maintenance cost. As a hydraulic sensor is arranged in the liquid cylinder body, the gas-liquid pressure cylinder has a real-time pressure monitoring function, can quickly and accurately feedback and display hydraulic pressure information, can carry out an early-warning prompt for abnormal pressure, and is convenient for a hydraulic system to maintain and find faults. The gas-liquid pressure cylinder is convenient to add oil and can monitor and feedback the hydraulic pressure in real time, all the operations are automatically completed during working, and the practicality is strong. The gas-liquid pressure cylinder is used together with low-speed and middle-speed maglev train braking systems, lowers the labor intensity of workers, and is convenient to maintain and reliable in work.