  In this paper, we try to improve the magnetogram calibration method of the
Solar Magnetic Field Telescope (SMFT). The improved calibration process fits
the observed full Stokes information, using six points on the profile of Fe
{\i} 5324.18 {\AA} line, and the analytical Stokes profiles under the
Milne-Eddington atmosphere model, adopting the Levenberg-Marquardt least-square
fitting algorithm. In Comparison with the linear calibration methods, which
employs one point, there is large difference in the strength of longitudinal
field $B_l$ and tranverse field $B_t$, caused by the non-linear relationship,
but the discrepancy is little in the case of inclination and azimuth. We
conclude that it is better to deal with the non-linear effects in the
calibration of $B_l$ and $B_t$ using six points. Moreover, in comparison with
SDO/HMI, SMFT has larger stray light and acquires less magnetic field strength.
For vector magnetic fields in two sunspot regions, the magnetic field strength,
inclination and azimuth angles between SMFT and HMI are roughly in agrement,
with the linear fitted slope of 0.73/0.7, 0.95/1.04 and 0.99/1.1. In the case
of pores and quiet regions ($B_l$ $<$ 600 G), the fitted slopes of the
longitudinal magnetic field strength are 0.78 and 0.87 respectively.
