Abstract: Coupled device with LED light source for fiber-optic illumination is often composed of lens group. Though the convergence spot of this system is small, the light loss of lens group is big. Due to the characteristics of LED light source and the big aperture of polymer optical fiber, an side installation for LED lamp and an optimization method that reflector was cutted and shifted were put forward,and a kind of coupled device with LED light source based on elliptical reflector was designed. Using the approximation algorithm that had been proposed by John O-Farrell, the elliptical reflector-s structure parameters for different eccentricities were calculated. Through comparing the coupling efficiency by combining with the simulation of fiber-s optical parameters, a group of structural parameters of efficient coupled device that the eccentricity matched the fiber diameter were obtained. Using this method, a coupled device with LED light source was designed which had a fiber diameter of 10 mm and numerical aperture of 0.5.The ideal coupling efficiency was up to 93.35%.