A single-longitudinal-mode pulsed Ho:YLF laser was demonstrated and studied experimentally at 2065.68 nm via injecting a unidirectional seed laser with double corner cubes to a Q-switched Ho:YLF power-oscillator. Up to 733-mW single-longitudinal-mode Ho:YLF laser with a structure of double corner cubes cavity is employed as seed laser with the advantages of narrow linewidth and high antimisalignment sensitivity. For single-longitudinal-mode injection-seeded Q-switched Ho:YLF laser, the output energy of 4.41 mJ is obtained with the repetitive frequency of 100 Hz, pulse width of 136 ns, and slope efficiency of 19.3%. The experimental results show that this method is a potential way to realize single-longitudinal-mode injection-seeded Q-switched Ho:YLF laser with narrow linewidth and high antimaladjustment sensitivity.