Lasers near the wavelength of 2 μm are located in the atmospheric transmission window and the strong absorption peak of water, and have important applications in medicine, LIDAR, material processing, and as pump sources for mid-infrared lasers. The thulium-doped fiber laser (TDFL) stands out as a critical light source capable of delivering high power outputs at this wavelength. In this paper, to address the problems of relaxation oscillation and inter-modal four-wave mixing in quasi-continuous wave (QCW) TDFL, the time and frequency-domain output characteristics of the laser are optimized by increasing the bias current, optimizing the length of the gain fiber, and changing the diameter of the fiber coiling, etc. The effects of different gain fiber structures on the fiber transmission modes are also investigated. The developed QCW-TDFL achieves a peak power of 894 W and an average power of 89.4 W at a central wavelength of 1939.2 nm with a pulse width of 100 μs, a repetition frequency of 1 kHz and a duty cycle of 10%, and obtains stable and controllable pulse output waveforms and spectral characteristics.