In this study, a master oscillator power amplifier (MOPA) system based on LCP is designed. The whole system is divided into several parts, including electro-optic intensity modulator, narrow linewidth continuous seed source and so on. In the specific design process, the nanosecond pulse signal can be converted, and then the corresponding Laguerre Gaussian light can be obtained. The core method used in this process is the spatial phase conversion method. Finally, the LP01 mode output of 20.1 W is obtained, and high stability is maintained. In addition, high quality radial polarized light output is obtained through LCP vortex wave plate. The repetition frequency and average power are 10 kHz and 19.5 W, respectively, and very high conversion efficiency and mode purity of 97% and 88.5% respectively are obtained. Therefore, it can achieve high power while meeting the purity requirements, showing broad application prospects.