Abstract: In order to understand the mechanism of drought stress affecting on spring maize, a field experiment was conducted by withholding water for 30 days during the period from jointing to filling. Main variables associated with photosynthesis including net photosynthetic rate(Pn), transpiration rate (T_r), stomatal conductance（G_s）, intercellular CO₂ concentration(C_i) and stem flow rate (SF) as well as leaf and root water potential were observed and their response characteristics to drought were investigated. The results indicate that G_s、P_n and C_i  respond slowly to mild drought and decrease quickly when drought aggravates and reaches moderate level .except for T_r responding quickly to mild drought. Further, with drought stress aggravating, the determination factors of photosynthesis rate is changed from stomatal factor to stomatal and non-stomatal factors. After rewatering, the above mentioned parameters recover to normal level and G_s、P_n and T_r show fast compensatory increases, while T_r dose not respond sensitively to increased soil moisture. In addition, daily amount of stem flow is not affected by mild and moderate drought stress but shows a compensatory rising after rewatering. Leaf water potential responds to drought stress slower than that of root water potential which restoration ability is better than leaf water potential.