Abstract: To clarify the dynamic characteristics of crop water supply and demand and identify regular drought periods in the saline-alkali areas of Hebei low plains, taking Huanghua City (coastal saline-alkali region) and Nanpi County (inland saline-alkali region) as representative counties, this study analyzed the temporal variations in potential evapotranspiration, effective precipitation, and water demand during the growth periods of winter wheat and summer maize. This analysis was conducted using daily meteorological data from 1980 to 2024, the FAO Penman-Monteith model, and the water balance index method. It compared water supply and demand differences across growth stages and identified critical drought periods using daily water balance indices. Results indicated that over the past 45 years, potential evapotranspiration in the study area had shown an upward trend, with annual growth rates ranging from 1.79 to 2.30 mm/a. Meanwhile, effective precipitation during the winter wheat growing season had decreased at rates of 0.66 mm/a (Huanghua City) and 0.71 mm/a (Nanpi County), exacerbating the imbalance between water supply and demand. Winter wheat experienced persistent water deficits throughout its entire growth period. The cumulative deficit during the heading stage reached 117.01–118.36 mm, with an average daily deficit intensity of 5.87−5.92 mm/d. Approximately one-third of the entire growth period was classified as severe drought or higher. Summer maize generally maintained favorable water conditions, experiencing only short-term water shortages during the grain filling stage. Two high-frequency drought periods were identified using daily-scale water balance indices: early to mid-March (around March 6 to 15 during the regreening stage) and early to mid-April (April 2 to 6 and April 13 to 17 during the jointing stage). Based on these findings, water management recommendations were proposed: Nanpi County could explore the phased complementary use of brackish water and rainwater, while Huanghua City is advised to prioritize irrigation methods centered on rainwater harvesting and efficient utilization. This study reveals the detailed processes of crop water stress at the daily scale. The identified critical drought windows and irrigation recommendations provide spatiotemporal reference points and decision-making insights for achieving precise water regulation through rainwater resource utilization and safe use of slightly saline water in this region.