The invention discloses a gas-phase reaction device for breaking gas-phase reaction equilibrium limitation through reactive distillation outside a tower and a preparation method of dicyclohexylamine.The preparation method, aiming at gas-phase reaction with balance limitation; reactants or intermediate products being light components; and products being heavy components, comprises following steps:enabling gas reaching reaction equilibrium at an outlet of a primary reactor to enter a rectifying tower (or a stripping tower); cooling heavy component products into a liquid phase; wherein most ofthe reaction raw materials exist in a gas phase; enabling tower top gas phase to enter a secondary reactor after cross heat exchange through a superheater, after reaction, carrying out cooled mixturecondensation and refluxing, enabling heavy component products to enter a tower bottom through the rectification effect, enabling light component reactants or intermediate products to continuously enter the secondary reactor for reaction, so that the whole reaction yield is greatly improved.