Abstract: An analysis of dynamics with changing topology for thehumanoid running robot is carried out. First, a coordinate system ischosen. Then the constraint equation and the Jaccobi matrix are derived and thedynamics equations of the robot in stance phase and in flight phase areobtained. Next, the identification equation in different phases isderived as the condition of the robot from one phase to another phase. Inaddition, the impact between a foot of the robot and the ground is analyzedwhen the robot contacts the ground from the air. Finally, a virtual modelof the robot is built by the software ADAMS and the validity of the methodis verified by the simulation for the virtual model of the robot.