Numerical study of inverse free-electron laser acceleration (IFELA) in the presence of a tightly focused laser beam is investigated in vacuum. In this article, we investigate the dynamics of an electron in the inverse free-electron laser (IFEL) with a planer wiggler field geometry. The numerical study on particle acceleration is carried out for tightly focused laser parameters as well as the tapering along the wiggler field. It is observed that the effect of tapering point along the undulator is crucial to maintain the IFEL resonance condition and to maximize the energy gain. The role of normalized laser field and of tapering point of planar wiggler magnetic field is examined on the electron acceleration. The role of pre-energy modulation of real electron-bunch and its acceleration will be planned in our next simulation work.