The field evaporation process and the annual rate of crop evapo-transpirations in the experimental fields under lbcal climatic conditions were calculated by means of an empirical formula.Comparing data obtained with average raining process and amount of annual rainfall in the same fields,the results of water balance in black soils under different crops were obtained.Using these results to evaluate the adequate water supply to crops,we found that soybean and corn had a rather good reliability of water supply,but as for the spring wheat it appeared somewhat shortage,and was apt to suffer from drought.The seasonal frozen layer in black soil played an important role in the regulation of water supply,and the spring thaw in the frozen layer was the main source of water in the earlier stage of plant growth.Factors affecting spring drought were studied and methods for prediction of shrine droueht were sueeested.