The invention discloses a synthetic method of heat-resistant N-methyl polysilazane liquid silicone rubber, comprising the following steps: polysilazane is used as a reinforcing filler to synthesize heat-resistant liquid silicone rubber, and by the utilization of thermodynamic properties of silazane and with the designed molecular structure as the target object, anion-catalyzed ring opening is carried out to synthesize n-methyl polysilazane; by using the synthetic product as a reinforcing filler, through dimethyldichlorosilane and ammonia water in an ammonia atmosphere and by using high-puritymethylbenzene as a reaction reagent, low molecular weight octamethylcyclotetrasilazane is synthesized; and the molecular structure design and controllable synthesis of polysiloxane are carried out according to the angle of silicon-nitrogen bonds and the molecular space. Since the proportion of N-methyl polysilazane added reaches 20% in the synthetic method of the heat-resistant N-methyl polysilazane liquid silicone rubber, the liquid silicone rubber is solidified due to excessive bulk viscosity and is in a solid state. Through comprehensive analysis, an appropriate proportion of N-methyl polysilazane can help effectively improve heat resistance and thermodynamic stability of liquid silicone rubber.