Abstract: This paper presents the study and the testing results of reducing heat flux in nitro-group-oxidizer-unsymmetrical dimethylhydrazine engine with additive methyl silicone. The relationship between heat flux reduction and improvement of rocket engine is discussed. The properties of additive methyl silicone and the mechanism of heat flux reduction in the thrust chamber are described. Analysis of testing results shows that the viscosity of additive silicone （SiOC2H6）n should be less than 13 centistoke at 20℃; when 1wt% Si is added into UDMH, there is slight improvement in the operational property of pro-pellant;and the total heat flux of the thrust chamber has been reduced about 33% .