Based on synthetic flux spectra calculated from theoretical atmospheric models, a calibration of temperature and metallicity for the dwarfs observed in the Beijing-Arizona-Taiwan-Connecticut (BATC) multicolor photometric system is presented in this paper. According to this calibration, stellar effective temperatures can be obtained from some temperature-sensitive color indices. The sample stars have colors and magnitudes in the ranges 0.1 < d − i < 0.9 and 14.0 < i < 20.5. The photometric metallicities for these sample stars can be derived by fitting SEDs. We determine the average stellar metallicity as a function of distance from the Galactic plane. The metallicity gradient is found to be d[Fe/H]/dz = −0.37 ± 0.1 dex/kpc for z < 4 kpc and d[Fe/H]/dz = −0.06 ± 0.09 dex/kpc between 5 and 15 kpc. These results can be explained in terms of different contributions in density distribution for Galactic models 'thin disk', 'thick disk' and 'halo' components. However, for the gradient in z > 5 kpc, it could not be interpreted according to the different contributions from the three components because of the large uncertainty. So it is possible that there is little or no gradient for z > 5 kpc. The overall distribution shows a metallicity gradient d[Fe/H]/dz = −0.17 ± 0.04 dex/kpc for z < 15 kpc.