An electro-optical Q-switched Nd3+: TAG laser is used as pumping source and a pure LiNbO3 crystal as optical parametric oscillator, its phase matching angle is 50? The wavelength is toned by varying the temperature of LiNbO3, and the single resonant tunable wavelength range is in 2.8~4.0m. Its output energy is ;about 0.3mJ/pulse and linewidth about 3cm-1 when the wavelength is 3.3m and the repetition rate is 10pps.