Mixed molybdenum tungsten disulphide (Mo<sub>x</sub>W<sub>1-x</sub>S<sub>2</sub>), a new member of the transition metal dichalcogenides, has drawn much research attention in the photonic devices. In this work, we demonstrate a Q-switched Tm-doped fiber laser (TDF) using Mo<sub>0.8</sub>W<sub>0.2</sub>S<sub>2</sub> polymer film as a saturable absorber (SA). Mo<sub>0.8</sub>W<sub>0.2</sub>S<sub>2</sub> is obtained by microwave-assisted solvothermal method and its nanosheets are embedded into a polyvinyl alcohol (PVA) film. The film SA is sandwiched between two fiber connectors and is inserted into the all-fiber TDF laser cavity. The total cavity length of TDF is 30m and a 4 m Tmdoped fiber is used as the gain medium. The TDF is pumped by a multimode 793nm laser diode (LD). Use the polarization controller (PC) to change the polarization states, a relatively stable Q-switched pulse train are realized when the pump power up to 2.17 W. The output power of the oscillator increase from 4.4 mW to 7.3 mW with the pulse repetition rate from 11.9 kHz to 15.7 kHz. In addition, the shortest pulse duration of 11.7 μs generated with the pump power of 2.26W.