The invention provides a dedicated ventilation device of a painless gastroscope, which ensures free breath and prevents reflux. The device comprises a hood provided thereon with two inlets and a gastroscope inlet therebetween, wherein the inlet to the side is a respiration inlet connected with a breathing machine, and the gastroscope inlet is connected with a sheathed gastroscope guide tube that has one end positioned in the upper part of the hood and the other end positioned in the lower part of the hood. The device further comprises an air sac at the external part of the front end of the sheathed gastroscope guide tube in the lower part of the hood, and the air sac communicates with an air injection pipe, wherein the other end of the air injection pipe is positioned in the upper part of the hood and communicates with an air injection valve. The invention can relieve syndromes caused by respiratory depression of various degrees due to general anesthetics, such as hypoxemia, severe respiratory depression, breath and cardiac arrest, and even death caused by non-timely rescue. The invention ensures efficient respiratory support without lightening the anaesthesia in consideration of the respiratory depression, and meanwhile prevents the occurrence of reflux and aspiration. Therefore, the invention can ensure the success of gastroscopy while providing respiratory support, thereby providing safety and convenience for the painless gastroscopy.