Based on the theory of quasi-three-level, a model of threshold pump power of Ho∶YAG laser was built and the formula of threshold pump power of Ho laser was derived. The relationship between the threshold pump power and the absorption efficiency of gain medium or the transmission of output coupler was analyzed. The mW-level threshold pump power of Ho laser can be obtained by optimizing parameters of Ho laser, which was pumped at 1 907 nm or wing-pumped at 1 930 nm. Furthermore, center wavelength lasing at 2 092 nm or 2 124 nm should be achievable by choosing an output coupler of suitable transmission.