In order to reveal relationship between temporal stability of soil water and corn ear weight under straw returning in black soil region, based on soil water content measured with TDR during June and September 2017 and corn ear weight measured with weighing method, the temporal stability of soil water under straw returning was firstly determined, and then the relationship between temporal stability of soil water and corn ear weight at the single scale and multiscale was quantitatively analyzed. The results showed that the temporal stability of soil water was increased with the increase of soil depth, and the sampling points in deeper soil layer (40～60cm and 60～80cm) which had higher soil water content had higher temporal stability; as soil depth changed, representative points of soil water under different situations were not identical, and the lowest, highest and average soil water contents for studied area could be determined with representative points of soil water content which could provide scientific guidance for estimation and regulation of soil water; the changing trend of correlation degree between temporal stability of soil water and grain weight per ear and axis weight per ear at multiscale was different from the one at the single scale, correlation degree between temporal stability of soil water in most soil layers and grain weight per ear and axis weight per ear at multiscale was more than the one at the single scale, and relationship between temporal stability of soil water and corn ear weight could be determined further with multiscale correlation analysis, which could provide theory basis for deeply revealing the influence of soil water on crop yield. Research results could provide theoretical foundation and guidance to estimate and manage soil water and increase crop yield.