In this paper, inverse dynamics of the H4 robot is addressed. Dynamics of parallel robots is one of a very complicated subject. Especially, for the real time control of the parallel robot, it is an important issue. The actuating torque would depend not only on a given trajectory but also on the mass properties of the arms, the rods, travelling plate, and external forces. Dynamics are useful for computer simulation, the design of suitable control equations, and the evaluation of the kinematic design of parallel robots. The detailed dynamic equations for the H4 robot are derived using Newton-Euler method. In the last section, the effect of the rod inertia is introduced using comparative study of those methods whether the inertia of the light rod can be negligible or not in the fast motion.