Traditional large-size direct-illumination structures for liquid crystal display (LCD) do not contain light guide plates. Though the uniformity meets the demand of LCD module, the whole thickness of the illumination system is difficult to reduce. With the development of white light emitting diode, many changes can be introduced in LCD for improving performances of system. In this paper, a design method based on that technique for direct illuminated LCD with light guide is presented. A LCD illuminating module was designed with this method, and uniformity can reach 86% which satisfied the illumination demand.