The invention discloses a mechanical grate type waste gasification incinerator with less conversion thermal efficiency loss and higher thermal recovery efficiency and a boiler system of the waste gasification incinerator. The mechanical grate type waste gasification incinerator comprises a gasification incinerator, the boiler system and a circulating air supply system, wherein the gasification incinerator comprises a feeding bin, a gasifier and a burnout furnace, a stockpiling sealing section is arranged between the feeding bin and the gasifier, a transition slag blanking section is arranged between the gasifier and the burnout furnace, and flue gas outlets are formed in the upper ends of the gasifier and the burnout furnace respectively. The boiler system comprises a boiler body, the boiler body is provided with a cyclone combustion chamber, a furnace chamber a and a furnace chamber b which are mutually communicated, a water cooling wall is arranged in the cyclone combustion chamber, a superheater is arranged in the furnace chamber a, an evaporator is arranged in the furnace chamber b, a steam drum is arranged at the top end of the boiler body, a steam-water inlet is formed in the steam drum, the steam drum is connected with water inlets of the water cooling wall and the evaporator and used for outputting water, steam outlets of the water cooling wall and the evaporator are connected with a steam inlet of the steam drum for backflow of steam, and a saturated steam outlet of the steam drum outputs superheated steam through the superheater.