To achieve better mixing effect for a gas-liquid metal two-phase flow and get higher flow velocities of liquid metal in a liquid metal magnetohydrodynamic (LMMHD) generator for improving its output power and efficiency of power generation, a nozzle-type mixer was designed and numerically simulated using ANSYS FLUENT. The results show that carbon dioxide gas makes the velocity of the liquid metal in the LMMHD generator channel increase by 409% under the liquid metal inlet pressure of 1.2 MPa and gas inlet pressure of 1.5 MPa, while the average volume fraction of liquid metal in the power generation channel is 0.39, the maximum output power is 5526.15 W and the maximum power generation efficiency is 43.6%. With the increase of the liquid metal inlet pressure, the flow pattern of liquid metal changes from droplet flow to film flow. In the research range of this paper, when the inlet pressure of liquid metal increases, both output power and generator efficiency increase first and then decrease.