  It is an indisputable fact that solar magnetic fields are force-free in the
corona, where force free fields means that current and magnetic fields are
parallel and there is no Lorentz force in the fields. While the force-free
extent of photospheric magnetic fields remains open. In this paper, the
statistical results about it is given. The vector magnetograms (namely,
$B_{x}$, $B_{y}$ and $B_{z}$ in heliocentric coordinates) are employed, which
are deduced and calibrated from Stokes spectra, observed by Solar Magnetic
Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS) are used. We
study and calibrated 925 magnetograms calibrated by two sets of calibration
coefficients, that indicate the relations between magnetic fields and the
strength of Stokes spectrum and can be calculated either theoretically or
empirically. The statistical results show that the majority of active region
magnetic fields are not consistent with the force-free model.
