The Lorentz force can be used to control the boundary layer flow of low-conduction fluids; however, its lowest control efficiency has become the main bottleneck in its engineering application. In order to enhance the control efficiency of Lorentz force, we need to study its potential control mechanism. In the present paper, the flow around hydrofoil when using Lorentz force has been simulated numerically by use of dual-time-step Roe method as well as studied experimentally in a water tank. Results show that the hydrofoil drag decreases sharply first and reincreases later, showing that the control effect of the Lorentz force is reduced with the increase of stream velocity, as well as the amplitude-change of the lift and drag; however, the lift increases continuously. The basic mechanism of this phenomenon is that the Lorentz force can form Lorentz force thrust, which increases the wall friction and decreases the pressure on the hydrofoil surface; at the incipient stage of control, the Lorentz force thrust decreases the drag and increases the lift immensely, soon afterwards, due to the action of Lorentz force, the drag increases with the increase of wall shear force and the lift increases with the decrease of upper surface pressure, so that the thrust can increase both the drag and lift.