The invention relates to a key groove sealing structure of a drum gear coupling. The key groove sealing structure of the drum gear coupling comprises shells and sleeves, wherein the shells are provided with inner teeth, the sleeves are provided with outer teeth, and each shell is connected with a shaft through a key. A water stop ring is arranged on the outer end face of each sleeve, wherein the water stop ring is connected with the outer end face of the sleeve in a sealed mode, the water stop ring is arranged on the shaft in a sleeved mode and is connected with the shaft in a sealed mode. According to the key groove sealing structure of the drum gear coupling, the keys connected between the sleeves and the shafts and key grooves are all sealed through the water stop ring structure, so that the seal performance is good, and water and other impurities can be effectively prevented from entering a gap. The key groove sealing structure of the drum gear coupling is simple and is installed in an insertion and interference fit mode, so that installation and assembly are both quite convenient.