The utility model discloses a water inflow-preventing quenching device of a steel cylinder. The water inflow-preventing quenching device comprises a base body, as well as a positioning mechanism, a quenching lifting mechanism, a transmission mechanism and a quenching slot which are arranged on the base body, wherein the positioning mechanism is fixedly arranged at the rear end of the base body; the quenching lifting mechanism is arranged at the upper end of the base body; the quenching slot is arranged at the lower end of the base body; the transmission mechanism is arranged on the quenching lifting mechanism; a gas-blowing pressing mechanism which moves synchronously with the quenching lifting mechanism and is used for pressing a cylinder port of the steel cylinder and a gas-blowing mechanism which is used for charging gas into the cylinder port of the steel cylinder are further arranged on the base body. According to the utility model, after a transmission roller rod transmits the steel cylinder to a gas-blowing quenching position, the gas-blowing pressing mechanism tightly presses the steel cylinder inlet, the gas-blowing mechanism starts blowing gas and then the quenching lifting mechanism descends and quenches. And therefore, quenching liquid is guaranteed to not enter into the steel cylinder; after the quenching is completed, the lifting mechanism is lifted to the position, the transmission roller rod rotates for transmitting out the steel cylinder, and a workpiece is transferred to the next process after the transmission is ended.