In this paper, the mechanism of intracavity optical parametric oscillator (OPO) is briefly analyzed. A high efficent and compact 1.57μm eye－safe intracavity optical parametric oscillator is developed, which is based on a non－critical phase－matched KTPⅡ crystal placed inside the resonator of a KD *P electronic－optical Q－switched (Ce, Nd):YAG laser by flashlamp pumping with water cooling. In experiment, the highest signal output 87.7mJ at 10Hz is obtained, the pulse width is about 7ns, the wall－plug efficiency is up to 5.8‰, and the OPO device is 410mm×130mm×80mm in size.