Numerical simulation of the gasoline engine working process is carried out with one dimensional and threedimensional software based on a natural aspiration direct injection engine with high compression ratio to analyze the trend and effect of the ultrahigh tumble intake system on combustion performance in combustion system of high thermal efficiency. Three kinds of in take port with different tumble ratio and four kinds of calculation cases are designed in the study. Comparisons of transient tumble ratio

transient turbulence energy

velocity field in cylinder

equivalence ratio

heat release rate and mean pressure in cylinder among different cases are made. Results show that the tumble ratio affects the distribution of the gas mixture in cylinder and the strength of the turbulence energy. Higher tumble ratio can help keep more energy stay near the top dead center

which can enhance the average turbulence energy in cylinder at spark time

affecting the combustion process including flame development and propagation and the engine performance. The piston with the pit can keep the turbulence energy at the center at different tumble ratios

which means that the turbulence energy around the spark plug is higher

accelerating the propagation of the flame. In the combustion system

when the tumble ratio increases to some extent

it is hard to enhance the average peak pressure in cylinder and better the engine performance. Thus

the excessive tumble ratio has little effect on engine performance optimization.