Pulsed fiber laser at 2-µm band has important applications in fields including material processing, environmental monitoring, and surgery. Mode-locking and Q-switching are two common working mechanisms of pulsed lasers, while the control of their existence and conversion in the same laser proves difficult. In this work, the theoretical model used in ultrafast laser optics is adapted for the conversion between mode-locked and Q-switched pulses. We proposed a method which introduces a feedback loop to control the conversion between the two regimes at 2-µm, revealed the laser dynamics during the transition process, and verified the feasibility of the method by simulation and experiment. This research provides a stable method to control the working regime of 2-µm pulsed lasers as well as a model for future research concerning gain variation in ultrafast laser dynamics.