A profiling float is an important observation device capable of acquiring ocean profiling data. In order to accurately control the vertical movement of the profiling float, a variable volume oil bladder buoyancy regulation system that can precisely control the oil volume was proposed, which included components such as an external oil bladder, a pressurized oil tank, a solenoid ball valve with good sealing performance, and a hydraulic pump with adjustable speed. Among them, draw-wire displacement sensor was used to collect the liquid level position of the pressurized oil tank in real time to achieve oil volume monitoring, and high-precision closed-loop feedback control of the volume of external oil bladder. By designing a hydraulic system with extremely low leakage, the buoyancy of the system can be stabilized for a long time in the standby mode. In order to accurately control the buoyancy regulation system, a mathematical model of the control system was constructed, a PID control algorithm was introduced, and the stability simulation was carried out by using Simulink. The experimental results show that the system can achieve precise control of buoyancy with a maximum overshoot of less than 1%. The stability and response speed are in line with expectations, which verifies the reliability of the control strategy.