To study the gas-liquid flow in liquid-ring vacuum pump and its vibration characteristics, the test system was developed for flow visualization and vibration monitoring. The flow structure was captured by high-speed camera, and the vibration sensors were mounted on the bearing house and the pump casing respectively. The study shows that the vibration amplitude trends of the bearing house and pump casing are both a quadratic curve during start-up period, and the vibration amplitude of the pump casing is closely related to the unstable gas-liquid interface. With the increase of impeller rotation speed, more and more bubbles penetrate to the liquid ring, and the wakes are becoming more intense. Under different operating conditions, the main vibration of pump casing is highly relevant to the transient gas liquid flow. The main characteristic frequencies vibration of the bearing house is caused by mechanical resonance. The vibration level of the bearing house is significantly higher than the pump casing at all conditions. The vibration level of the pump casing increases with the decrease of flow rate and the increase of rotation speed for the transient flow. The vibration level of the bearing house reaches the maximum when the rotation frequency is consistent with the natural frequency.