With Magnetospheric Multiscale Mission (MMS) observation of a magnetic flux rope of ion scale in magnetopause, we apply the single-point method presented by Rong et al., [2013] to study the magnetic field structure of flux rope. The calculated geometric parameters, e.g. axis orientation, helical handedness, current density, curvature radius, and boundaries of flux rope show well consistency with those derived from the multi-point methods. Thus, the single-point method of Rong et al., [2013] is reliable for studying the interior field structure of magnetic flux rope and could be applied widely to single-point spacecraft missions that examine the dynamics of flux rope.