A design method for Light-emitting Diode (LED) Compound Elliptical Concentrator (CEC) is proposed based on optical extent, in order to satisfy specific emergent angle and high efficient illumination in short distance. Firstly, the CEC generatrix equations are derived according to the optical properties of LED light source and the optical extent conservation theory in non-imaging optics. Then the front and rear surface types are analyzed in the light of the edge-ray principle and the ray tracing theory in geometrical optics. Finally, the designed system is ray tracing simulated in optical software ZEMAX. The results show that, the emergent angle is 51.6° and the light energy utilization efficiency reaches 69%, in the scope of 8 mm×8 mm detector that is 4mm away from the CEC exit aperture. The reasonableness of the method is proved by comparing the simulation results with the theoretical calculation. Using the small size-concentrator is an effective way to realize system’s miniaturization and simplification.