By analyzing crop water stress index(CWSI) for monitoring water stress with both Idso's empirical model and Jackson's theoretical model applied in summer maize in North China Plain,the CWSI variations and relationship between soil water content,leaf water potential and the empirical & theoretical CWSI models were studied.The results showed that the values of empirical CWSI model were below the range of 0-1 frequently while the values of theoretical mode seldom behave so,and the daytime variation of the empirical CWSI model based on canopy temperature was bigger than that of the theoretical model.The CWSI models could be used for guiding irrigation schedule while the theoretical model was more reasonable due to its more interrelations with summer maize leaf water potential.