Abstract: To suppress 1064nm line and 1338nm line,utilizing the dichroic mirror technology,a Nd:YAG quasi-CW laser operating at the single wavelength of 1318.8nm was developed.The output power of 122W was obta ined at a pump power of 2100W with the total efficiency of 5.8%,and the slope efficiency of 8.22%.The unstability of output power was less than (±5%.)The threshold power was about 500W.The 1318.8nm Nd:YAG laser with simple construction can work stably,which is of great value to laser therapy and nation al defence.