Method for preparing modified betaine type amphoteric surfactant used for tertiary oil recovery

The invention provides a method for preparing a modified betaine type amphoteric surfactant used for tertiary oil recovery. In the method, sodium bisulphite, epichlorohydrin and long-chain alkyl tertiary amine serving as raw materials are subjected to ring-opening reaction and quaterisation to form the amphoteric surfactant used for displacement of reservoir oil. Because the amphoteric type oil displacement agent for tertiary oil recovery is a modified sulfonate betaine type surfactant, the modified betaine type amphoteric surfactant for tertiary oil recovery of the invention has higher performance compared with the conventional surfactants. The surfactant of the invention has the advantages of typical and mature method, high interfacial activity, high efficiency and environmental protection and high universality.