Microfluidic chip detection system based on laser-induced fluorescence was analyzed. Fluorescence collecting effidency of the system was developed,in which refractive index of medium in microchannel and that between the microchip and objective lens were considered. A new optical arrangement of laser-induced fluorescence with high fluorescence collecting efficiency was presented,which adopted an ordinary microscope objective without long working distant and high numeric aperture. Converging exciting laser bevel illumination with high deflecting angle was achieved by a prism cemented on the microchip. Elliptical sphere lens coated with reflecting film was used as a reflector to attain collecting of backward fluorescence. Refractive index matching liquid was added to reduce the fluorescence divergence angle from the microchip surface. The system reduced the requirement for working distance of the collecting objective lens greatly. Compared with traditional fluorescence detecting structure, fluorescence collecting efficiency could be improved up to about 6.3 times. The experimental result by ray-tracing is about 4.3 because of the influence of structure of objective lens and the cross section profile of microchannel.