The sapphire fiber thermometer ranging from the room temperature to 1800℃ is described. It uses a specially grown sapphire fiber as the thermometer probe. The end part of the sapphire fiber is doped with Cr 3+ ion by means of the laser heat pedestal growth (LHPG) method and coated with some high radiant material to constitute a mini fiber cavity. Techniques of fluorescent lifetime detection and the radiance intensity detection were used. Growth of the end doped sapphire fiber is introduced. Analysis is made on the temperature dependence of fluorescence of the end doped sapphire fiber as well as the signal interference between the fluorescence and the thermal radiance. Experimental system of the thermometer and the preliminary experimental result are presented.