Abstract: The gas-lift pump has been adopted to enhance the natural circulation capability in the conceptual designs of lead-bismuth alloy cooled reactors such as ADS and LMFR. The natural circulation capability and the system safety have been obviously influenced by the two phase flow characteristics of liquid metal-inert gas. The numerical research was performed to evaluate the natural circulation capability of lead-bismuth alloy cooled ADS with gas-lift pump. Based on the drift-flux flow model, void fraction prediction model and frictional pressure drop prediction model were adopted in the numerical simulation. The effects of the gas mass flow rate, the gas quality, the bubble diameter and the height of rising pipe on natural circulation capability of gas-lift pump were analyzed. The results show that in bubbly flow pattern, for a fixed value of gas mass flow rate, the natural circulation capability increases with the decrease of the bubble diameter. In the bubbly flow, slug flow, churn flow and annular flow patterns, with the gas mass flow rate and the gas quality increase, the natural circulation capability increases initially and then decreases. As the height of rising pipe increases, the natural circulation flow rate goes up. The flow parameters influence the thermal hydraulic characteristics of the reactor core significantly. Therefore, in practical engineering application, the gas mass flow rate, gas quality, bubble diameter and rising pipe height are very important parameters for the design of gas-lift pump systems. The present work is helpful for optimizing the design of the natural circulation cooling system by gas-lift pump.