Abstract This paper describes how to reconstruct the excitation force of a typical engine from the measured velocity data at mounting points. The theoretical analysis is carried out at first to get the equations for the force re-construction. It indicates that with the full information of velocity (amplitude and phase) at all mounting points, the excitation force and moment at the center of gravity of engine can be exactly retrieved. Due to the difficulty in measuring the absolute values of the phases, further study is carried out to investigate the possibility to reconstruct the force and moment only with the velocity amplitude as well as the phase difference between three directions at each mounting point. A group of overdetermined equations are derived and solved with optimization methods rather than the conventional numerical method. It is found that with combination of genetic and gradient-based algorithms, the excitation force and moment of engine can be well-established based on the velocity spectra and phase angle difference of velocities.