The experimental design plans were determined on analyzing main factors to affect infiltration capability of muddy water. Based on the experimental data, it is considered that the main factors are infiltration time and soil clay content, the concept of soil clay index was presented to denote soil clay content in muddy water, and muddy water infiltration expression was presented. The concerned parameters in the expression are regarded as the optimal variables and determined by binary system code method of the genetic algorithm. It showed that muddy water infiltration expression was relatively accurate, and the reason for muddy water infiltration differing from rinsing was the clay in muddy water, and the more the soil clay index was, the less the accumulation infiltration amount was.