Plant phenology is extremely sensitive to climate change. Shift in the timing of plant phenological events serves as a powerful biological indicator of climate change. In the context of global warming, plant phenology has changed accordingly. These changes, in turn, affected the climate system, and exacerbated or mitigated climate change. In particular, plant phenology is also a key parameter of ecosystem model, and it is of great significance to understand the mechanism of phenological changes for improving the simulation precision of the model. Although plant scientists have always been interested in the physiological basis of controlling plant phenological stages, the previous studies mainly focused on the monitoring of phenological changes and the statistical relationship between phenological changes and climatic factors. Few studies have been conducted on the ecophysiological mechanisms of plant phenological changes. The data of phenology and corresponding ecophysiological observation of spring maize was obtained from field simulation experiment that controlled water at jointing stage and rewatering at tasseling or silking stage, respectively. We analyzed the phenological characteristics of spring maize and its relationship with the change of ecophysiological factors, and revealed the ecophysiological mechanism of phenological changes of spring maize. The results are as follows:(1) After the water control at jointing stage, the filling stage was prolonged and the milking stage was delayed (9 days) regardless of rewatering at tasseling or the silking stage. It indicated that the phenology of spring maize would be affected by water control significantly at jointing stage even though rewatered at tasseling or silking stage, and spring maize phenology had memory for early water control. (2) The leaf net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), and relative chlorophyll content (SPAD) of spring maize showed a trend of decrease-increase-decrease with time. The P_n, T_r, G_s, and SPAD reached the local minimum at tasseling stage under the water control at jointing stage. The P_n, T_r, and G_s reached the local maximum at silking stage and SPAD reached the local maximum at filling stage after rewatering at tasseling or silking stage. The leaf water potential (LWP) presented a downward trend over time, but only slowed down after rewatering, reflecting that LWP might indicate the memory of early water stress. (3) Path analysis and decision coefficient analysis showed that P_n was the most important factor affecting phenology. The relative soil water content (RSWC) affecting LWP was main control factor. The phenology was only affected by the accumulated change of P_n, indicating that there was a trigger threshold of accumulated P_n in phenology changes of spring maize. The results could improve the ecophysiological cognition of the phenological changes and provide a basis for accurate prediction of the phenological changes of spring maize.