With good machine performance and spectrum characteristic, Ho:YAG crystal has become one of the choices for high-repetition-frequency 2 μm laser. In order to acquire high efficiency and high power 2 μm Ho:YAG laser with high-repetition-frequency, radiation mechanism of singly-doped Ho3 + laser are analyzed. And the calculation model of conversion efficiency in high-repetition-frequency Ho:YAG laser is established through rate equation. The effects of the parameters such as output coupler transmittance, laser mode size, ratio of pump-laser mode and Ho-doping atomic number fraction, on the conversion efficiency in high-repetition-frequency Ho:YAG laser are analyzed by this calculation model. The design scope of those parameters is also put forward. The theoretical simulation results are verified through experiments.