A gas injector used for semiconductor equipment includes a housing shell, a rotating main shaft and a gas output distribution unit. The rotating main shaft is covered with the housing shell, and includes a plurality of magnetic fluid seals and a plurality of gas transmission tubes. The gas output distribution unit is coupled to a top end of the rotating main shaft, the gas output distribution unit being connected to a ceiling and a susceptor. The gas output distribution unit includes a plurality of boards spaced at intervals between the ceiling and the susceptor, thereby resulting in a plurality of gas output layers for outputting corresponding reaction gases.