A high efficiency Tm3+-doped fiber seed source system has demonstrated. The pumping laser and output laser in the optical fiber distribution were analyzed. High performance output laser would be obtained by reasonable design of laser parameters, selecting the optimum length of gain fiber, and increasing injection power. Tm3+-doping concentration of 7.5×1024 m-3 and the optimum length of gain fiber of 2 m were used in the experiments. The continuous wave laser with output power of 5.01 W and the beam quality of M2x = 1.35, M2y = 1.51 was obtained by fiber coil diameters of 10 cm and injection power of 17.61 W. A slope efficiency and conversion efficiency were up to 36.2% and 28.4%, respectively. The fiber length of 1 m, 1.5 m, 2 m, 2.5 m, 3 m were chosen in the experiments, and the effects of different fiber lengths on the output characteristic were researched. The laser loss was reduced, and the conversion efficiency and beam quality were improved effectively by selecting the length of gain fiber and Tm3+-doping concentration reasonably. Theoretical analysis and experimental results show that a higher output power can be achieved by increasing the injection power. It provides a strong experimental foundation for further researching on high power Tm3+-doped pulse fiber amplifier by using this Tm3+-doped fiber laser as a seed source system.