Abstract: Comprehensive researches of the spectral characteristics on the domestic Tm-doped double cladding fiber with hexagon inner cladding cross section are presented. When the fiber is pumped by 1064nm laser, the bright blue light is observed. The up-conversion spectra are measured and the mechanism is analyzed. The fluorescent spectra and the laser spectra are also measured when the fiber is pumped by a 785nm LD. The fiber lasers operated at ～2m wavelength are obtained with three different output coupler mirrors and with two fiber lengths of 4.5m and 2.2m, respectively. The maximum output power is 5.1W and the slope efficiency is 41.9%. The experiment results are analyzed.