Abstract: In order to obtain the quantitative contribution of various functions of stabilizer, the author divides them into two parts, i.e. the composite binding effect (Eb) and the filling effect (Ef). The composite binding effect includes three actions, i.e. the hydrating action (Ah), the exciting action (Ae) and the ion exchanging action (Ai). The methods to calculate the two parameters (Eb and Ef ) and the strength index are proposed. The test results indicate that the Eb and Ef exist at the same time. The two effects rise continuously with the age, but the speed and the amount of their rise are different. The three actions (Ah,Ae,Ai) are studied. The test results indicate that the three actions exist before the silt and the stabilizers are mixed. Finally, a physical model to explain silt stabilizing is built.