Human motor behavior can be generated by distributed system. In this study, human standing-up motion is focused as an important daily activity. Especially, 13 muscle activation of lower body and trunk measured during human standing-up motion is decomposed into small numbers of modules of synchronized muscle activation called muscle synergy. Moreover human musculoskeletal model is developed with four rigid body segments based on dynamics and anatomical characteristics of human body. Forward dynamic simulation with the developed model showed that four muscle synergies had their own contribution toward body function: bending forward, moving the center of mass forward, extending whole body, and decelerating the center of mass. Results also indicated that combinations of four modules of synchronized muscle activation could generate human standing-up motion rather than controlling individual muscles.