Abstract: In the Tm, Ho laser system, the optimum transmittance and pulse duration was practiced using the rate equations theory. In a 2 m ring resonator, the Tm, Ho: LuLF laser material was side-pumped from three directions and Q-swtiched of acoustic-optic device. The output coupler of 20% and 30% transmittance was compared. In the 20% transmittance coupler, it was demonstrated that the Q-switched laser pulse energy of 58.0 mJ with an optical to optical efficiency of 1.45%. The 62.9 mJ energy was obtained with the optical to optical efficiency of 1.57% in the 30% transmittance coupler. And the 48.7% of dynamic to static ratio was obtained in the same injection. The pulse duration was 417.2 ns when 3.25 J energy was injected. The experiment values are in consistent with the simulation results.