It is difficult to confirm the pressure effect on oil and gas generation and organic matter maturation,because the fluid pressure in sedimentary basins changes during geological history.High pressure simulation experiment is a good method to study the pressure effect,but different researchers come to different conclusions by different experiment methods.The geological case studies show that increasing pressure can suppress or retard petroleum generation and organic matter maturation.Different viewpoints on pressure effect are introduced in this paper,and the future work should be developed in pressure effect study and its meaning are also put forword.