Due to the existing research of the cylinder gasket is limited to the assembly working conditions, the stress and strain of the cylinder gasket under the cylinder pressure condition and its influence on the engine block deformation are not considered. This paper aimed at a gasoline engine "cylinder head- cylinder gasket-cylinder body-bolt" sealing system, built the 3D solid model and the finite element model of the assembly, and calculated the stress and strain of the cylinder gasket under the cylinder pressure and the deformation of the engine block. In addition, based on the calculation results, this paper put forward the optimization scheme of the cylinder gasket structure, re-established the simulation model, and get the calculation results. The calculation results showed that the cylinder pressure had influence on the sealing performance of the cylinder gasket, and the influence of cylinder pressure should be taken into consideration when designing the cylinder gasket. When the cylinder pressure was applied, the overall contact stress of the cylinder gasket had decreased, and the whole remaining height of the gasket had increased. At the same time, the cylinder head generated impact load to the cylinder head, and the deformation of the cylinder reach the maximum. The cylinder gasket could not meet the requirements of manufacturers. After the structure optimization, the minimum contact stress of all convex bars was improved from 22.239Mpa to 28.596MPa; the minimum contact stress of the semi convex bars was improved from 5.438Mpa to 7.778Mpa. So the sealing requirement of the host plant was satisfied. After the structure optimization, the compaction thickness of the cylinder gasket was more uniform. The average compaction thickness was decreased by 0.024mm, but it could still meet the design requirements. Besides, the structure optimization of cylinder gasket had also improved the deformation of the cylinder head and body.