High-power, high-conversion-efficiency and tunable continuous-wave (CW) near-infrared external-cavity pumped singly resonant optical parametric oscillator (SRO) was proposed. OPO based on a quasi-phase-matched (QPM) nonlinear crystal was a very effective technology to obtain the short-wave near-infrared tunable laser sources. CW laser at 532 nm was used as the fundamental laser source to drive the OPO in the cavity. The QPM crystal was a multi-grating MgO-doped stoichiometric periodically poled LiTaO₃(MgO:sPPLT). The widely tunable SRO output signal wavelength ranging from 807 to 879 nm and idler wavelength ranging from 1352 to 1567 nm were achieved by combination of poling period tuning and temperature tuning with four different periodically poled gratings from 8.3 to 8.6 μm. By means of using single resonant of idler light, the output power of the signal (821 nm) was 3.1 W at a pump power of 5.4 W with the efficiency of 57.4% was achieved. Under an incident pump power of 13.6 W, a maximum signal output power of 6.8 W at 821 nm was obtained with the period of 8.6 μm.