The invention provides a slag and water vacuum separation device of a slag conveyor for a gasification device. At least one slag and water hole is formed in a bottom plate of an uphill surface of the slag conveyor, a grating plate is mounted on the slag and water hole, and a filer cloth and a screen mesh are sequentially mounted on the grating plate; a vacuum water collecting tank communicated with a vacuum dehydrating device is arranged at the lower part of the grating plate; at least two rectangular slag and water holes are formed in the bottom plate of the uphill surface of the slag conveyor in the longitudinal direction; the vacuum dehydrating device comprises a vacuum vapor separation tank provided with a water discharging pipe at the bottom. The vacuum vapor separation tank is connected with a vacuum pump which can vacuumize the vacuum vapor separation tank. The slag and water vacuum separation device has the characteristics that the structure is simple, the water content of discharged ash slag can be greatly reduced, the phenomenon that a slag car leaks water and fine slag is eliminated, the environment of a slag conveying site can be greatly improved, severe pollution to environment in the ash slag pouring and conveying processes is prevented and the like.