This paper presents new methodology to solve the inverse dynamics of the humanoid robots. The objective is to calculate the joints' torque in order to select in optimal way the robot's gait and actuators. The main advantage of the method is its simplicity that everyone can implement it easily using common software packages which are not prepared for the humanoid robot modeling, like Matlab Robotics Toolbox. The inverse dynamics solving is divided in two parts, the upper and lower extremities (including the body). At the same time it is necessary to analyze separately the phases on simple and double support. The first one doesn't present so much difficulty by using conventional manipulator dynamic modeling. But during the double support phase the modeling is performing for each leg separately by using balanced mass distribution between them. This distribution is based on the reaction forces calculation for each supported leg. The developed method had been applied to the 21 DOF and 1.4 m height Rh-0 humanoid robot under development at the Robotics Lab. of the University Carlos III of Madrid.