The self-reinforced MQ crosslinking agent containing methoxy group（MMQ） was synthesized by hydrosilylation reaction. And then, used in the condensed room temperature vulcanization (RTV) silicone rubber.The structure and microscopic morphology of the RTV rubber were characterized，the effects of methoxy group content（mass fraction）on the hydrophobic property，mechanical properties, thermal stability property and transparency property of the condensed RTV silicone rubbers were investigated. Moreover, the reinforcing effects of MMQ, octyl MQ silicone resin (OMQ) and epoxy modified MQ silicone resin (EMQ) on the RTV silicone rubbers were investigated. The results show that MMQ and the condensed RTV silicone rubber were prepared successfully. The reinforcing effects of MMQ are superior than OMQ and EMQ. With the increase of methoxyl content,the hydrophobicity, mechanical and thermal stability of the RTV silicone rubbers are improved markedly, but the ultraviolet light transmittance is decreased. In conclusion, the condensed RTV silicone rubber has an optimum comprehensive performance when the methoxy content is 7.83% in MMQ,the contact angle of 108°, the water absorption rate of 2.2%, the tensile strength of 4.3 MPa, the elongation at break of 261%, the Shore A hardness of 42 A，the maximum degradation rate temperature of 413.6 ℃，the residual rate at 800 ℃ of 23.6% and the ultraviolet transmittance at 350 nm of 80.67%.