  Magnetic field extrapolation is a fundamental tool to reconstruct the
three-dimensional magnetic field above the solar photosphere. However, the
prevalently used force-free field model might not be applicable in the lower
atmosphere with non-negligible plasma \b{eta}, where the crucial process of
flux rope formation and evolution could happen. In this work, we perform
extrapolation in active region (AR) 12158, based on an recently developed
magnetohydrostatic (MHS) method which takes plasma forces into account. By
comparing the results with those from the force-free field extrapolation
methods, we find that the overall properties, which are characterized by the
magnetic free energy and helicity, are roughly the same. The major differences
lie in the magnetic configuration and the twist number of magnetic flux rope
(MFR). Unlike previous works either obtained sheared arcades or one coherent
flux rope, the MHS method derives two sets of MFR, which are highly twisted and
slightly coupled. Specifically, the result in the present work is more
comparable with the high-resolution observations from the chromosphere, through
the transition region to the corona, such as the filament fibrils, pre-eruptive
braiding characteristics and the eruptive double-J shaped hot channel. Overall,
our work shows that the newly developed MHS method is more promising to
reproduce the magnetic fine structures that can well match the observations at
multiple layers, and future data-driven simulation based on such extrapolation
will benefit in understanding the critical and precise dynamics of flux rope
before eruption.
