An apparatus for preventing and controlling secondary generation of hydrates in a wellbore during depressurization exploitation of offshore natural gas hydrates includes a gas recovery pipe column, a water recovery pipe column, a gas-liquid mixed transportation pipe section, a data collecting and processing unit, and a reaction control apparatus; according to characteristics of different exploitation pipe columns, three injection pipelines and three monitoring points are arranged to predict dynamic changes in a secondary generation risk of the hydrates throughout the wellbore; measures for preventing and controlling the secondary generation of the hydrates are taken at different pipe column positions by the integrated utilization of inhibitor injection, heating for pipe columns, the additional arrangement of electric submersible pumps, and other methods.