Abstract: Based on the multi-body dynamics and Lagrange equation, the differential equation of rigid motion of the four-bar placer jib of a concrete pump truck is deduced. With the numerical solution to the equation, the rotation angles between every two bars and the jib end track are analyzed. A dynamical simulation software is used to develop the rigid motion model for the jib, in which the same kinematic parameters are selected to those in numerical solution, thus comparing the track as the result of simulation with that numerically solved. It is shown that the two results are basically in conformity with each other. The multi-body dynamics is therefore proved useful to express the movement equation of the placer jib of concrete pump truck with each and all dynamic behavior expressed exactly.