Abstract: A solute transport equation is presented,in which the reaction of ion exchange between,water and rock is considered.A new mathematical model of sea water intrusion is also presented.In this model,the exchange cation Na⁺ and Ca²⁺ are used as simulated factor and the cation exchange of Na⁺-Ca²⁺ between water and rock in aquifer during sea water intrusion is considered.This model is applied to simulate sea water intrusion in Huangheying areas,Longkou City,Shandong Province,the simulated result agree well with the observed data.This demostrate that the presented solute equation is correct and the presented model is reliable.