The maopingxi rockfill dam with asphalt concrete core is one of the topmost dam with asphalt concrete core in the world. Because the filling materials as changed

the experimental data is very limited

and the parameters for numerical analysis is not nicety

so it is difficult to evaluate the probable state of stress-strain in the dam body. To obtain the parameters of the filling materials

the monitoring data and optimum theory and finite element method are used for back analysis in this paper. Then

the stress and displacement of the dam are computed and analyzed by using the parameters. The results show that the rule and the value of stress-strain by back analysis accord with the monitoring data very wel1.