Abstract: The paper have built up an auxiliary designing software GRLT suitble to sun light environmental analysis of different greenhouses in China by using computer simulation techniques. The software was used to analyse temporal and spatial distributions of direct solar radiation within greenhouse and determine greenhouse structure with optimal light trans-missivity. The GRLT software runs on 386,286 and IBM-PC/XT as well as its compatible computer under support of MS-DOS 3. 30 above operating system. The user interface is friendly and operation is convenient in the GRLT. It is an auxiliary tool for optimal design of light transmissivity in greenhouse.