Abstract: The vibration coupling pumped concrete fluid with conveying pipes occurs typically in the concrete placing process of a concrete pump truck. A differential equation of motion was derived for the coupling, then a natural frequency curve during concrete conveying at different flowrates and under different fluid pressures was given via dimensionless discretization. It was revealed that the first-order and second-order natural frequencies both decrease with the increasing pumping-out pressure, and the natural frequency increases gradually with the increasing pumping-out speed of concrete. So, with the fluid pressure and concrete flowrate determined properly, the concrete placing process can be completed avoiding the operation in the range of resonance, thus reducing the fatigue damage to arm supports. The conclusions provide theoretically the reference for selecting the pumping-out pressure and speed especially the operating frequency of concrete pump.