The theoretical analysis and experimental research of the optical parametric oscillator (OPO) based on periodically poled LiTaO3 (PPLT) crystal are presented. The wavelength tuning curves of PPLT-OPO are calculated through the coupling equations of the three-wave mixing. The output characters of signal singly resonant oscillator (SSRO) and idler singly resonant oscillator (ISRO) are studied. When the pump power of the NdYAG 1.064 μm laser is 48 W with a repetition rate of 5 kHz, the output powers of 3.9 μm laser from SSRO and ISRO are 5.78 W and 5.07 W, and corresponding conversion efficiencies are 12% and 10.6% respectively. The near-field distribution and beam quality of the 3.9 μm laser from ISRO are better than those from SSRO.