The present paper deals with the requirements of paddy soils for tillage and through study on the relattonship oetween the pnysicai properties of soil and the growth of crops. Experiment results revealed the great effect of the soil mechanical disturbance on water potential, which indicated that it is a major factor resulting in soil puddling; moisture content and the capacity of effective moisture were higher in topsoil than in subsoil, which shower that soil puddling increases water retention. The linear negative correlation between moisture content and bulk density was statistically significant (n=62,r=-0.909^**). Thus long-term zero-tittage soils can suvolv insufficient water for crop erowth. The most favorable codition for wheat. growth on paddy soil was the soil moisture suction ranging from 0.02 to 0.5 bar. Because field capacity is higher than plastic limit, plowing and pulverizing the soil following rice inevitably leads to soil puddling. The best growth of rice appeared at the bulk densities ranging from 1 to 1.3 g/cm², which was similar to those after the flooding of the soil of zero-tillage following wheat. Therefore, zero-tillage is suitable for paddy soil under cropping system of rice and wheat. The grain yields of rice and wheat under zero-tillage were increased by 142.5 kg/ha and 367.51kg/ha, respectively as compared with traditional tillage, according to the results obtained from 52 experiments of rice and 23 experiments of wheat. The physical properties were not deteriorated in permeable paddy soils under zero-tillage for three years and in waterlogged paddy soil for two years.