The invention provides a heat-conducting silica gel sheet for heat dissipation of a lithium battery of a new energy automobile and a preparation method thereof, belonging to the field of heat dissipation materials for lithium batteries. The heat-conducting silica gel sheet is prepared from the following raw materials in parts by weight: 30 to 40 parts of vinyl-terminated methyl silicone oil, 1 to3 parts of alpha,omega-hydroxyl-terminated polydimethylsiloxane, 2 to 5 parts of polymethylhydrosiloxane, 0.1 to 1 part of tetramethoxysilane, 20 to 30 parts of graphene doped boron nitride, 10 to 20parts of fumed silica, 1 to 5 parts of microcrystalline wax, 0.05 to 0.2 part of dibutyltin dilaurate, 5 to 10 parts of KH-570, 20 to 25 parts of methyl vinyl MQ silicon resin, 0.1 to 0.5 part of acetenyl cyclohexanol, 5 to 10 parts of allyl glycidyl ether, 1 to 2 parts of zinc dimethyldithiocarbamate, 0.01 to 0.02 part of a hydrosilylation catalyst and 100 to 200 parts of water. The heat-conducting silica gel sheet has good heat conduction performance, the heat conduction coefficient is larger than or equal to 7.21 W/(m.k), the insulation performance is excellent, the breakdown voltage is larger than or equal to 24.63 kV, and certain mechanical elasticity is achieved; and the heat conduction silica gel sheet is not prone to crushing and fracturing, and can meet the requirement for heat dissipation of the lithium battery of the new energy automobile.