In order to evaluate the effect of different tillage methods on soil moisture of maize accurately, the research monitored the soil moisture during the whole growth period under conventional tillage with returning straw and subsoiling with returning straw in real time and analyzed the dynamic changes of soil moisture at different time scales. The results indicated :(1) Subsoiling could increase the soil water content of 10cm, 30cm and 70cm respectively by 7.66%, 8.74% and 6.37%.The soil moisture of 30 cm soil layer under the two tillage methods showed a big difference. (2) At hourly scale, it was found that the variation of each layer soil water content of two tillage methods was quite different after raining. When the soil moisture reached its peak after rain , the soil water content of 10cm during the conventional tillage would dip at night, and that during the subsoiling tillage would gradually decline during one day.(3) In addition to the seedling stage, the subsoiling could significantly improve the soil moisture of other growth stages of which jointing and filling stage to enhance the most,respectively at 5.00% and 6.03%.（4）Compared with conventional tillage,subsoiling could increase yield 5.70%.