Argentum nanorods (ANRs) with the absorption wavelength of 2 μm are prepared and employed as a saturable absorber in a 2 μm passively Q-switched laser. A laser diode (LD) pumped by 2 μm passively Q-switched laser is designed with a compact linear cavity. When the absorbed pump power is 5.73 W, average output power of 118 mW, repetition rate of 24.32 kHz and pulse width of 1.455 μs are obtained.