The invention relates to a flame-resistant sealing material for an opening of a building penetrated object and a preparation method thereof. The provided silicone sealant has better flame-resistant effect, larger expanding rate, lower flame spreading factor, low smoke and no poison. The provided preparation process has simple preparation method and lower consumption in the production process. The expanding type flame-resistant silicone sealant comprises the following raw materials in parts by weight: 100 parts of alpha, omega-dihydroxyl-polyorganosiloxane, 1-50 parts of polydimethylsiloxane, 120-400 parts of flame-resistant filler, 5-20 parts of expanding filler, 2-15 parts of cross-linking agent, 0.2-4 parts of silane coupling agent and 0.1-5 parts of catalyst, wherein the alpha, omega-dihydroxyl-polyorganosiloxane has the structural formula shown as above, n is equal to 50 to 2,000, and R is CH3-, CH3CH2- or phenyl. The preparation method comprises the following steps: (1) preparing a base material; and (2) compounding the sealant.