One dual-pumped tunable optical parametric oscillator (OPO) is designed. With a 1.065 μm single-frequency pulsed fiber laser pumping the periodically poled domain MgO-doped lithium niobate (MgO:PPLN) and a reflective volume Bragg grating narrowing the oscillation signal linewidth, the idler signal linewidth is reduced from 38 nm at free oscillation to 0.42 nm, the oscillation threshold is reduced to 6.7 W, and the mid-infrared laser output with a high conversion efficiency is realized. By adjusting the temperature and angle of the volume grating, a 230 GHz tunable output of idler light is realized and the beam quality factors in the horizontal and vertical directions are 1.8 and 1.9 respectively when the output power of idler light is 2.5 W.