Abstract: The relationships between soil wetting pattern and crop-root distribution as well as plant growth under drip irrigation are the theoretical bases for determining the soil wetted percentage in design of drip irrigation system. Based on the field experiments with the plastic mulched drip irrigation, diverse soil wetting patterns were gained by regulating the dripping discharge on dripping plots with the identical irrigation water. By which the distribution of cotton root system was studied as well as the growth process of cotton plant in the inner and outer rows. The experimental results indicated that the narrower-deeper-type soil wetting pattern in consequence of small dripping discharge resulted in lower uniformity of horizontal soil moisture, therefore resulted in lower distribution uniformity of cotton root system in soil and plant growth in field. While the wider-shallower-type soil wetting pattern in consequence of larger dripping discharge resulted in higher uniformity of horizontal soil moisture and higher distribution uniformity of cotton root system in soil and plant growth in field. The wider-shallower-type soil wetting pattern was appropriate to the plastic mulched drip irrigation technique.