To improve the fluorescence detection sensitivity of multi-core fiber,based on the spatial conduction theory model of multi-core fiber,the effects of the number of multi-core fiber,the core radius of excitation fiber,the core radius of receiving fiber and their numerical aperture on the coupling efficiency of multi-core fiber are analyzed.To improve the coupling efficiency,the curvature radius and spacing between non-spherical lenses in the coupling system are designed and optimized.Based on the analysis and optimization of the parameters,a multi-core optical fiber fluorescence quantitative detection system is constructed.Quantitative tests are conducted on different concentration gradients of Rhodamine 6G solution.Compared with direct coupling,the designed multi-core optical fiber coupling system shows an increase of 80.171% and 95.314% in excitation and emission light coupling efficiency,respectively,starting from below 10%.The lowest detection concentration is reduced to 2.08759551×10-9nM/L,and the fluorescence intensity at this concentration is increased by 4.5 times compared to direct coupling.The feasibility of the multi-core optical fiber coupling system is further validated,demonstrating that increasing the optical coupling system can effectively improve the sensitivity of fiber-optic fluorescence quantitative detection and meet application requirements.