Single-mode coupling is a key technology in the fiber -coupled optical system. At present , there are still some problems in the process of single-mode coupling , which directly affect the results of single-mode coupling. In order to obtain better single-mode coupling results , the single-mode coupling efficiency of the fiber-coupled optical system is analyzed and studied in this paper. Firstly , a fiber coupled optical system is designed according to the princi- ple of single mode coupling , and the transmitter and receiver are designed. Then the single mode coupling model of the fiber coupled optical system is constructed. The test results show that the single -mode coupling model of the design system has obvious advantages , and the coupling efficiency has been significantly improved , which provides a valuable reference for the related fiber coupled optical system.