To minimize the elements inserted in the cavity of 2μm band tunable laser and reduce the cavity loss, a special designed prism based on the disperse property of LiNbO₃ crystal was used as tuning and Q-switching element . Two faces cut at Brewster＇s angle make the prism work well as tuning element. In a flash-lamp pumped Cr-Tm：YAG 2μm laser with the LiNbO₃ prism, active Q-switching operation was realized at room temperature, while the tuning range of 1.95 -2.08μm was obtained with the prism. The repetition rate of the Q-switched laser was 1-5 Hz. The experimental result shows that the Q-switching and tuning method is valid.