Through collecting the test data of large number of groundwater samples ,the result has been found that most of deep groundwater belongs to sodium bicarbonate type water in the area such as Hengshui and Dezhou of the central North China Plain. By use of theory of groundwater cycle and geochemistry, the paper discussed about the origin of sodium bicarbonate type water formed in the central North China Plain .The results show that the groundwater of the area is from precipitation, it has the characteristics of leaching witch is affected by post-water-rock interaction and positive ion exchange action, witch makes the calcium in groundwater be absent and the sodium enrichment, the sodium bicarbonate type of water is formed. Meanwhile, the fluoride ions in groundwater enrich and their content increase in the alkaline environment.