To keep micro projection system compact and highly efficient, an illuminating system is proposed based on LCoS and LED. This system follows the principle of Kohler illumination. By modifying Kohler illumination system and setting the rational stop, uniformity lighting zone can be got on the LCoS plane. Besides, this system becomes simple and compact. Spherical lens and aspherical lens are used in this illuminating system respectively. And simulation results show that illumination efficiency is 86% for spherical lens and 95% for aspherical lens. When using aspherical lens, transmission efficiency of the whole projection system is 9.94% and spatial uniformity is above 90%. The thickness of optical module is less than 9 mm.