Active fiber with high rare earth ion doping concentration has always been the key component of high-performance single-frequency fiber lasers, and silicate glass can be used to fabricate highly doped active fibers with excellent unit gains. Here, highly doped silicate glass with the thulium ion doping concentration of 8 wt.% was prepared by a high-temperature melting process, and its spectral characteristics and fluorescence lifetime were measured. Based on McCumber theory, the emission cross section of the glass was calculated. By the method of rod-in-tube, fiber preforms were prepared, and then the highly thulium-doped silicate glass fiber of 7/125 μm was drawn. Based on low-loss specialty fiber fusion splicing, the fiber unit gain was measured, and linear-cavity fiber lasers based on 2 cm and 8 cm novel thulium-doped fibers were investigated, where 1950 nm laser output of hundred-milliwatt-level power was obtained. This work has shown that under such a high doping concentration of 8 wt.%, which is the highest thulium doping concentration to date, thulium ions still have good luminescence properties in this novel glass host. The homemade highly thulium-doped glass fiber in this paper can be used to fabricate high performance single-frequency fiber lasers.