Henan Province is a main grain crops producing area in China, and water requirement trends of the main grain crops is an important basis for agriculture water saving and yield increasing. Based on the daily meteorological data from 18 stations in Henan Province during 1958 and 2013, reference crop evapotranspiration (ET0) and water requirement of winter wheat and summer maize in growth period were estimated by using FAO Penman-Monteith equation and crop coefficient. Time series analysis was used to analyze temporal distribution characteristics of ET0 and water requirement. Kriging of ArcGIS was introduced to draw the maps of ET0 and water requirement that could present a clear spatial distribution of that, and the causes of water requirement change were manifested by path analysis method. The research results showed that the value of ET0 in Henan Province ranged from 672mm to 977mm, and the average values were 807.0mm per year and 2.2mm per day, which was decreased in recent 62 years. The maximum ET0 appeared in the northwest and southeast of Henan Province, and ET0 showed a significant difference around the western area. The water requirement of winter wheat and summer maize were 390~562mm and 314~426mm, respectively. The irrigation requirement of winter wheat and summer maize were 350~525mm and 243~368mm, respectively. The index of irrigation requirement of winter wheat and summer maize were 0.77~0.90 and 0.66~0.83, respectively. The main grain crops irrigation requirement index of Henan Province tended to increase with the latitude and longitude, and summer maize had less dependence on irrigation than winter wheat. When each meteorological factor was removed respectively in sensitively analysis, the reliability of the regression equation was estimated by the remained eight meteorological factors. The main meteorological factors that influence water requirement of the main grain crops were temperature, vapor pressure, sunshine duration, maximum temperature and wind speed.