Abstract: A heat gun with an extendible/retractable safe heatproof sleeve comprising of: a housing composed of two hollow half-housings abutted and connected with each other, a muzzle of the heat gun has on the front end thereof a portion with a reduced caliber that has two lateral sides provided each with an axial recess which has an engaging portion; and a heatproof sleeve being a hollow housing, the housing has on each of two lateral sides thereof a sheet extending rearwardly, the sheet is provided on the inner side thereof with a protrusion, so that when the heatproof sleeve is slipped over the front end of the heat gun, the two sheets of the heatproof sleeve extend into the two axial recesses on the portion with the reduced caliber, the engaging portions can engage the protrusions, the heatproof sleeve thereby can slide on the portion with the reduced caliber on the front end of the heat gun and will not drop.