The invention relates to a reactor for preparing toluene diisocynate by a gaseous phase method and an operation method. The reactor is of a tubular reactor (8), wherein a central injector is arrangedin the middle of the tubular reactor and provided with a cone-shaped deflection baffle and a nozzle; and a deflection baffle is arranged on the pipe wall of the tubular reactor. Charging air current Apasses through an inlet (1) of the central injector (9) and enters the tubular reactor (8); charging air current B passes through an inlet (3) of the tubular reactor (8) and enters an annular space (4) between the central injector (9) and the tubular reactor (8); and air current A and air current B are two reactive materials. The invention provides the reactor or preparing toluene diisocynate bythe gaseous phase method and the operation method so that air reactant is turbulent in lower flow velocity, prompts the mixed range of the reactant to be shortened, thus reducing the time of the reactant retained in the reactor and the generation of the solid deposition on the wall of the reactor.