We demonstrate the strong optical bistability of a 2μm continuous wave Tm，Ho：YLF laser end pumped by a 792nm fiber-coupled laser diode. The quasi-three-level rate equation theoretical model is given under consideration of the energy transfer upconversion and ground state reabsorption effects. The bistable output of Tm，Ho：YLF laser is predicted theoretically by solving the coupled rate equations and the mechanism of the bistability output is analyzed. The bistable output is also studied experimentally. When the laser crystal is at 253K，the width of the bistable region is 1.6W and the jump power at the tujump point is 82.5mW. The theoretical results are in agreement with the experimental results，showing that the theoretical model is reasonable.