The effects of injection pressure on methanol atomization, air-fuel mixing, combustion and emissions were studied by three-dimensional numerical simulation based on the glow plug piloted direct-injection pure methanol engine. The results show that the increase of injection pressure will lead to the uniformity of in-cylinder mixture and the decrease of in-cylinder average temperature and pressure. The ignition occurs at the end of electric plug and the flame propagation shows a law different from diesel and gasoline engine. The mixture in the combustion chamber pit near the end of electric plug burns out first and then the flames spread to the surrounding space under high injection pressure. The higher injection pressure will lead to the higher formaldehyde content in expanding process, but it will also lead to the less formaldehyde residual in the exhaust. Compared with  the formaldehyde content of exhaust process, that of the expansion process can be negligible. Increasing injection pressure is beneficial to increase engine expansion power and improve power performance, but too high injection pressure will lead to premature combustion which will deteriorate power output.