The invention discloses an in-situ synthesis method for a nano tin dioxide/carbon nano tube composite material, which mainly uses an inorganic tin salt, a carbon nano tube and an alkali source as raw materials. The experimental process mainly comprises the steps of precursor preparation, hydrothermal reaction, precipitate washing and drying and the like. The in-situ synthesis method for the nano tin dioxide/carbon nano tube composite material has the advantages that: a hydrothermal method is adopted to realize the in-situ deposition and the growth of the nano tin dioxide on the surface of the carbon nano tube; the obtained SnO2 nano particles have small and uniform particle size (less than 10nm), are well-crystallized, are uniformly coated on the surface of the carbon nano tube, and are tightly combined with the carbon nano tube; the composite material has potential application prospect in the aspects of a gas sensor material, an anode material of a lithium ion battery and the like. The method has no addition of any surface active agent, has simple and easily-obtained materials, simple process without pollution, short preparation period, mild reaction condition and low cost, and is suitable for large-scale production, so the method is an environment-friendly synthesis method.