Using the data of the water samples of seawater intrusion monitoring in the coastal area of Laizhou Gulf,Shandong Province, and adopting the method of linear regression conducting in respective groups of intrusion degree, the author made a study on the relation between series of hydrochemical indexes and the Cl^- content, which involves 13 indexes including some main hydrochemical compositions of the water and the water quality indexes for irrigation.So the changes of the hydrochemical indexes in the process of seawater intrusion are shown by a series of linear regression equations with different slopes and relation coefficients. The analysis results also show the difference of seawater intrusion in the southern and eastern of coastal regions of Laizhou Gulf,the author considers that it is mainly because of the difference in the intrusion sources (current seawater or coastal underground salt water), salinization history and its affecting degree in the different parts of the coastal regions of Laizhou Gulf.