The present study proposes the method to closely predict the change in the slack of the clothes and its time-dependent variation along with the motion of the human body when modifying the patterns, by the numerical analysis through the visualization as the pseud-color map of the distance between the body and the cloth obtained by using the cloth simulation. The sensory evaluation in the various postures using one-piece dresses manufactured of the same pattern as used in the cloth simulation was carried out, and was compared with the result of the simulation to verify the evaluation of comfortableness by the cloth simulation. We evaluated clothing fit of the dresses in four postures, i.e. stand, squat, elevation, and anterior elevation, for two kinds of patterns of one-piece dresses with different bust sizes by the sensory evaluation as well as the cloth simulation. Body sites to evaluate were chosen as anterior and posterior of bust line, armhole, and waist line. By the cloth simulation, we obtained the average distance between the body and the cloth at each body sites as a quantity of the slack of the clothes. From the sensory test, the slack was evaluated as six ratings of the tightness by two test subjects of almost the same figure. The correlation coefficients between the quantity of the slack by the cloth simulation and the rating by the sensory evaluation were 0.617, 0.482, 0.800, for squat, anterior elevation, elevation postures, respectively. The time-dependence of the slack was shown to have a close relationship to the ease felt by human by examining the change in the slack of the clothes along with the motions from standing to each posture.