Abstract：Based on the research of classification and features of some typical soft rocks in a certain major project in Guangdong province，the authors design a series of tests for the interaction between soft rocks and water. Two typical rocks distributing in south China area，silty mudstone and mud siltstone，in natural state or saturated for 1，3，6 and 12 months，are studied to obtain variation regularities of concentration of cations，anions and pH value of solution and the dynamic evolution regularities of solution components for different soft rocks. The results show that during the saturation process，the pH value of the solution declines，the solution turns from light alkalescence to acidity，and the rates of that transformation are 2%～46%. Meanwhile，it¢s pointed out that the critical turning point of the interaction between water and rock appears at the time of 3 month. In the first 3 month，the exchanging and adsorption action of positive and negative ions are all active，the concentration of the ions declines during the reaction process，and in the following 3 month，the reaction gradually weakens，and the consistency of ions presents an ascending and stable trend. The concentration of ions in the reaction between soft rock and water are generally coincident with two types of curves，exponent curve and curve of dynamic stability equation. No matter what regularity the dynamic process is consistent with，it will ultimately turn to a stable state. In addition，the concentration of F－ and Mn2+，Al3+，Fe3+，Zn2+ in the tests on the two kinds of soft rock，almost maintains stable value，which suggests that these ions almost do not participate in the reaction between rock and water.
