Based on the simulated experiment data of winter wheat and corn in growth boxes,the variability of hydraulic resistance in the soil-plant system was analysed from aspects of diurnal changes and long-term changes of transpiration rates in this paper.The results indicated that hydraulic resistances in the plant were relatively large at low transpiration rates,decreased as transpiration rates increased and approached a constant value at higher transpiration rates.The effect of effective soil water potantial on hydraulic resistances was also studied.