Liquid metal magnetohydrodynamic (LMMHD) generators can generate electricity from the movement of liquid metal in an external magnetic field, without any mechanical moving parts. They can be applied in scenarios that require a highly reliable generator, including harvesting ocean wave energy and space nuclear power generation. However, in practice, the presence of end current in LMMHD generators limits the generator efficiency to a relatively low level, which restricts their wide application. After analyzing the generating mechanism of the end current, we report herein a method to optimize the external magnetic field that cancels the electrostatic field with the motional electromotive force and suppresses the end current in LMMHD generators. We use two-dimensional numerical simulations with the proposed method to demonstrate its effectiveness, which we validate with three-dimensional numerical simulations. Both the two- and three-dimensional numerical results show that this method should suppress the end current in the LMMHD generator, thus cutting the internal joule heating nearly in half and improving the generator efficiency by 9.5%. This work provides in-depth insights into both the generating mechanism and the suppression of the end current and contributes to the development of high-efficiency LMMHD generators.