Abstract: Abstract: Maize planting in northern region of China plays a vital role in the crop production in China, and it occupies a large proportion in total grain production and planting area in China. Meanwhile, northern region of China is prone to drought and the drought normalization happens in this area seriously, which restricts the steady development of maize. The data used in this paper included daily weather data of 217 meteorological stations in the 14 provinces (municipalities, or autonomous regions) in northern region of China from 1961 to 2010 and crop, soil, field management data of spring maize. Based on the total precipitation during the growing season of spring maize we divided the study area into 6 precipitation zones (Ⅰ-Ⅵ) with the interval of 100 mm, and then analyzed the effects of drought of different grades occurring in main growing stage on grain yield of spring maize in northern region of China by using the crop water deficit index as the agricultural drought index and the agriculture production systems simulator (APSIM) as the research method. The results showed that the yield reduction of spring maize caused by drought in northern region of China had a decreasing trend from west to east, and the precipitation distribution led to the differences of damage degree in each area directly. The precipitation during growing season of spring maize in Zone Ⅰ located in western region (including Xinjiang, western Inner Mongolia and northern Gansu) was below 100 mm, and the natural precipitation couldn't meet the need of growth and development of spring maize, so the drought risk of planting spring maize under rainfed conditions in western oasis irrigated agricultural area was great, and it needed to energetically develop water-efficient irrigation in this area. While the precipitation during growing season of spring maize in Zone Ⅵ located in southeastern region (including Southern Jilin, eastern Liaoning, southern Henan and southern Shaanxi) was above 500 mm, and the natural precipitation could meet the requirements of spring maize growth and development basically, so production in eastern rainfed agricultural area would be less affected by drought, and it was difficult to reflect the influence of drought grade difference on production accurately. In addition, the ratio of the station with yield reduction had a decreasing trend with the increasing of yield loss degree; from jointing to tasselling stage, the yield reduction in northern region of China was between 0 and 50%, and there were 37.3% of stations with the yield reduction of between 0 and 10%, and only 4.1% of stations with the yield reduction of between 40% and 50%. Drought happening from jointing to tasselling stage of spring maize will cause serious influence on grain yield, and the yield reduction in this stage is higher than that from tasselling to maturity stage. Besides, the discrete degree of yield reduction in this stage is also higher than that from tasselling to maturity stage. The influence degree of drought of each grade on crop production is different; from jointing to tasselling stage, the interquartile ranges of yield reduction caused by drought are extreme drought (20.1%-33.6%), severe drought (12.0%- 20.3%), moderate drought (6.3%-15.2%) and light drought (4.7%-11.6%), respectively.