A passively Q-switched solid-state Tm∶YAG laser with MoS2 as saturable absorber is reported. In this laser, a 785 nm narrow linewidth diode laser is taken as pump source, a plano-plano cavity is used, and MoS2 nanosheets are served as saturable absorber. Passive Q-switching can be achieved successfully in 2 μm wavelength region. When the absorbed pump power is at 2.02 W, the Q-switched laser pulses are obtained with the maximum average output power of 421 mW, the minimum pulse width of 423 ns, the pulse repetition rate of 49.36 kHz and the maximum pulse energy of 8.53 μJ. The results indicate that MoS2 is a kind of saturable absorber that can be used in solid-state laser in 2 μm wavelength region. Furthermore, it provides a potential way to obtain 2 μm pulse laser.