Laser diode (LD) side-pumping and intracavity-doubling technology is an available method to achieve high power, high stability and low cost continuous wave (CW) green laser. To meet the demand in the fields of laser color display, laser processing, optical data storage, laser medical and scientific research, an efficient high power diode-side-pumped intracavity-doubled CW green Nd:YAG/KTP laser has been developed successfully. By using plane-concave-plane resonator of three mirrors, and KTP of Ⅱ-type phase-matching for frequency doubling, a maximum of 18.7 W CW 532 nm green laser is obtained when the 808 nm pump laser power is 180 W, and the optical-to-optical conversion efficiency is 10.4%. The power stability of the laser is measured at output power of 15.4 W. During an hour measurement time, the output power instability is less than 0.5%. The output beam exhibits a smooth Gaussian-like profile in the far field and the beam transfer factor is measured to be less than 7 measured by knife-edge method at different output power.