A 3.705 μm compact,highly stable optical parametric oscillator (OPO) based on engineering application was reported.The method of combining semiconductor cooling technique,forced convection cooling technique and heat pipe technique was adopted to effectively manage the waste heat generated from pumping process of the main oscillator power amplifier (MOPA) structure of the Yb-doped fiber pumped module.Then the coupled pump light was injected into the PPMgLN crystal,which was precisely temperature controlled by a constant temperature oven.When repetition rate was at 55.56 kHz,average output power of 1.78 W at 3.705 μm line-polarized mid-infrared laser was obtained with 120 ns pulse width,the power instability was better than 1.5% and light-light conversion efficiency was 12.6%.