A liquid-nitrogen-cooled Tm, Ho:YLF laser is constructed with a 10-mm-long Tm(6%) and Ho(0.5%) codoped yttrium lithium fluoride crystal pumped by a laser diode operating at 792 nm. The laser output power is improved by cooling the Tm, Ho:YLF crystal from 300 to 77 K. When the crystal is kept at 77 K, the laser threshold pump power is 230 mW, the slope efficiency is 27.4%, and the maximum optical-tooptical efficiency is 19.9%. At the same time, the relation between the input power and the output power at different temperatures is obtained.