A gas injector and cover plate assembly includes a cover plate, a gas injector and a ceiling. The cover plate includes cooling fluid channels. The gas injector is configured to be located on the cover plate, and includes a gas distributor, a fluid-cooling gas transmitter, gas spraying plates and a conducting cone. The gas distributor distributes gases and a gas transmitter cooling fluid. The gas distributor includes a gas conduit for introducing a first gas. The fluid-cooling gas transmitter connects the gas distributor to introduce the gas transmitter cooling fluid to form cooling fluid walls and the first gas and the gases. The gas spraying plates and the conducting cone are located beneath the fluid-cooling gas transmitter.