The invention discloses a gas conveying device and a deposition method for silica-based polycrystalline silicon membrane deposition. The gas conveying device comprises a main gas conveying tube, a central conduction tube and a secondary gas conveying tube, wherein the main gas conveying tube is a reducing pipe of which the diameter of the upper part is large and the diameter of the lower part is small; the upper end of the main gas conveying tube is sealed; a gas inlet is formed in the lower end of the main gas conveying tube; the secondary gas conveying tube is supported by a reinforcing rod; the upper end of the secondary gas conveying tube is sealed; the lower end of the secondary gas conveying tube is communicated with the part above the diameter variable part of the main gas conveying tube through the central conduction tube; a plurality of gas outlet holes are respectively formed in the side surfaces of the main gas conveying tube and the secondary gas conveying tube. The deposition method comprises the following steps: (1) loading the gas conveying device on a vertical furnace, and connecting the gas inlet with a mass flowmeter and a silane gas source; (2) setting the temperature, the deposition pressure and the silane flow inside a deposition cavity; and (3) introducing a silane gas, and depositing a polycrystalline silicon membrane on a silica-based substrate. The 8-inch silica-based polycrystalline silicon membrane deposited by using the gas conveying device and the deposition method disclosed by the invention is very good in impurity absorbing property, and the purposes of process simplification, quality improvement and cost reduction are achieved indeed.