Supercharged boiler installation is widely applied in the main power plant of large and medium-sized ships for its high furnace volume heat release rate and small volume.The objective of this paper is to analyze the mechanism affected gas heat conduction and convection under pressure increased using the theory of molecular dynamics and properties of fluid molecules.And convection heating surface has been studied in this paper using the standard methods of Prof.Illes and the Soviet Union with supercharge ratio changed.The two methods calculation results including heat transfer coefficient，gas flow rate and gas density are compared with each other respectively.It is obtained that increased frequency of molecular collisions，decreased mean free path and larger gas density caused by pressure increased make the convective heat transfer process enhanced.And the calculation results demonstrate that differences between the two methods can be neglected under the low load however the heat transfer coefficient calculated with method recommended by Prof.Illes can be 1.3 times compared with the Soviet Union method when the pressure is close to 0.3 MPa.