Abstract: Experimental results from 1988 to 1990 in Heilonggang area in Hebei Province showed that in rainfed cotton field straw mulching could adjust soil temperature,reduce soil evaporation and inhibit weeds.It also had effects on promoting soil bioactivities and increasing soil fertility.Cotton yield was significantly increased with the increase of the amount of straw used.In the experiment the highest cotton yield was achieved at rate of 450kg/mu straw mulching.The time of straw mulching had also affected the cotton yield.The best season for straw mulching was at the bud stage from the results.