  We present a careful assess of the forced field extrapolation using Solar
Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) magnetogram.
The convergence property is checked by several metrics. The extrapolated field
lines below 3600km appear to be aligned with most Halpha fibrils observed by
New Vacuum Solar Telescope (NVST). In the region where magnetic energy far
larger than potential energy, field lines computed by forced field
extrapolation still consistent with the patterns of Halpha fibrils while
non-linear force free field (NLFFF) results show large misalignment. The
horizontal average of lorentz force ratio shows the forced region where
force-free assumption is failed can reach the height of $1400-1800km$. The
non-force-free state of the chromosphere is also confirmed by recent radiation
magnetohydrodynamics (MHD) simulation.
