A high conservation efficiency periodically poled LiNbO₃ (PPLN) optical parametric oscillator (OPO) based on the plano-convex unstable resonant cavity is demonstrated. The OPO is pumped by a Q-switch quasi-continuous-wave Nd : YVO₄ with a wavelength of 1064 nm. The thermal effect of the nonlinear crystal and the mode distribution under the plano-convex cavity are analyzed. Through temperature tuning, the wavelength of the signal laser covers 1471.4 to 1510.4 nm. When the temperature is 30°C, the repetition rate is 30 kHz, and the pump power is 5.7 W. A PPLN-OPO based on a plano-convex cavity generates a 1471.4-nm laser with a maximum output power of 1.09 W and pulse duration of 17.14 ns. The highest pump-to-signal conversion efficiency is 28.71%. When the repetition rate is 40 kHz, the highest conversion efficiency of 29.29% is achieved at the pump power of 2.8 W.