This study focuses on the analysis of the higher harmonic wave moments (around the seabed) on a vertical cylinder under the action of focused wave groups. The moment is known to be more nonlinear than the horizontal wave force; however, it is not very much investigated in the literature due to the difficulty of measuring accurately the mudline moment. We analysed the carefully measured wave loads from the tests in the Kelvin tank in the University of Strathclyde where a four-phase method is employed to extract the harmonic wave loads. The mudline moment shows a ‘Stokes-like’ underlying harmonic structure similar to the horizontal force. An approximation model is established to estimate the harmonic moment from the linear moment component. The model requires the nonlinear horizontal force coefficients and the moment arm of each harmonic. The moment arm for each higher harmonic is found from the measured forces and moments. The approximation model is demonstrated to be successful from both the measured data and numerical simulation.