Near-field acoustic holography (NAH) based on the boundary element method (BEM) is a powerful tool for noise source identification which is the premise of noise control. For large-scale structures, the measurement aperture should be large enough to ensure that the reconstruction results are accurate. However, the layout of field points often cannot meet the conditions necessary for reliable measurements. The patch NAH methods proposed in previous literature do not explore the influence of the initial and extrapolated aperture on the reconstruction of the vibration velocity. In this paper, the field distribution modes are redefined by the BEM and applied to extrapolation technology. First, the sound pressure of the field points on an expanded hologram is obtained by a data extrapolation method. The expanded data can then be used to reconstruct the vibration velocity of the structure and the sound pressure in the sound field via BEM-based NAH. A modified Tikhonov regularization is utilized in the inverse process. Different sound sources with simple or complex radiated sound fields are used for simulations to explore the influence of the initial and extrapolated aperture on the reconstruction. The application scope of the proposed extrapolation technology is identified and the conclusions are verified by experiments.