The invention relates to a sleeve distributed gas phase phosgenation reactor and a method for synthesizing isocyanate. The reactor is composed of a multi-layer sleeve distributor and a tubular reactor body, at least four layers of paralleled sleeves are arranged on the distributor in a coaxial manner, the abreast lower ends thereof are connected with the tubular reactor body, the upper ends thereof are stranded fluid feeding channel composed of non-equant round tubes with different heights, the height which at least doubles the diameter of the tubular reactor body is reserved for the inlet pipe of the sleeve arranged at the outmost layer to the lower end of the distributor, organic amine, inert components and phosgene can enter respective sleeve which is favor of controlling mixing, or the mixture of organic amine and inert components and phosgene can respectively enter a two-layer sleeve channel for alternate recycle which can easily satisfy the closely initial flow speed to reduce the difference of stay time, and the sleeve arranged at the outmost layer is used by phosgene. The reactor design in the invention and the operation method can effectively control the reaction speed, inhibits adverse reaction from occurring and reduces coking in the inner wall of the reactor.