Bioelectrical impedance analysis (BIA) is widely used for human body composition estimation for its easy and noninvasive operation. Body composition estimation based on BIA is usually developed with statistical analysis of experimental data for a special group of people. The error in the estimation, therefore, is extremely large. Based on electrical models for human body cells and Cole-Cole theory, a new method and corresponding BIA system are developed in this paper for measuring human muscle distribution of legs. Muscle distribution model for legs is developed with MRI data of human subjects. The relation between muscle and impedance distributions is then established. Different from the traditional cylinder body model and statistical estimation, the background of this method is the high correlation between MRI data curves of different subjects (r>0.9). Better estimation of leg skeletal muscle mass can be obtained by this theory. At the same time, the author introduces the half-analysis procedure into human body composition estimation. The validity of this method has been proved by DXA preliminarily.