Abstract: High energy green laser has significant applications in various scientific research and industrial fields, such as laser medicine, laser processing, optical parametric oscillator, ocean exploration, laser display and titanium gem laser pump source. Especially in the field of processing, the rapid development of electric vehicles and chip industries in recent years has made the processing methods of some special materials such as copper and silicon carbide more and more concerned. Compared with infrared lasers, the use of green lasers for processing these materials is more advantageous. Benefit by the wavelength of green light, copper can absorb 40% of green light at room temperature and only 5% of infrared light, so it is more reliable and efficient to process copper with green laser. In addition, green laser can be combined with water jet for water guided laser processing. Water guided laser machining using laminar flow guided light water jet instead of focusing light spot has obvious advantages in the depth of material processing ability. In addition, due to the cooling and scouring effect of water jet, there is almost no heat affected zone on the surface of processed materials, and the workpiece surface is clean and green. Therefore, this paper designs and studies a long-nanosecond-pulsed high-power green laser, with an output power more than 100 W, pulse duration more than 200 ns and fiber-coupled output, which can be directly combined with the waterjet nozzle to carry out the research of the corresponding water-guided laser processing equipment and the research of related processing technology. The whole laser can be divided into four parts, namely 1 064 nm long nanosecond pulse seed source, fundamental frequency dual-pass amplifier module, LBO crystal cavity frequency doubling module and fiber coupled output module. In the part of seed source, a 150 W side pump module was used, combined with acousto-optic Q switch, and the 245 ns long pulse laser output was successfully realized at 10 kHz refrequency by lengthening the cavity length and reducing the transmittance. However, this kind of long pulse width seed has the problem of low power. By using two 300 W side pump modules combined with dual-pass polarization multiplexing amplification technology, the fundamental optical power was increased from 15 W to 193 W at a repetition frequency of 10 kHz, and the average beam quality factor M2=9. In the subsequent frequency-doubling part, a class of non-critical phase-matching LBO crystal was used to obtain a 532 nm laser at 10 kHz refrequency of 109.5 W, pulse width of 205 ns, frequency doubling efficiency of 56.7%, and average beam quality of M2=16.4 through the way of out-of-cavity frequency doubling. After that, the optical fiber coupling of 200 μm (NA=0.22) was carried out. CCD was used to observe that the diameter of the coupling spot under the 50 mm focusing mirror was about 155 μm. Finally, the optical fiber coupling output of 532 nm green light of 101.6 W was successfully achieved, with coupling efficiency of 92.3% and power fluctuation of about 0.83%(RMS) within one hour.