Abstract: Assuming that the ship was at head sea，the phenomenon of the encounter frequency scattering was occurred by ship’s longitudinal velocity vibration. On the basis of the Froude-Krylov hypothesis，the coupling motion equations were obtained. Hydrodynamic coefficients of the coupling motion equations were calculated by Strip Method. The accuracy of results from numerical method was validated by theory method. The effects of ship scattering intensity and scattering frequency on the pitch and heave coupling motions were analyzed independently. The synthetical effects of the encounter frequency scattering on the pitch and heave coupling motions were obtained. The results of analysis show that the pitch and heave coupling motions can be weakened by increasing of ship scattering intensity and scattering frequency.