  We present the photometric calibration of the Beijing-Arizona Sky Survey
(BASS) and Mayall z-band Legacy Survey (MzLS), which are two of the three
wide-field optical legacy imaging surveys to provide the baseline targeting
data for the Dark Energy Spectroscopic Instrument (DESI) project. The method of
our photometric calibration is subdivided into the external and internal
processes. The former utilizes the point-source objects of Pan-STARRS1 survey
(PS1) as the reference standards to achieve the zero points of the absolute
flux for individual exposures. And then the latter revise the zero points to
make them consistent across the survey based on multiple tilings and large
offset overlaps. Our process achieves a homogeneous photometric calibration
over most of the sky with precision better than 10 mmag for g and r bands, 15
mmag for z band. The accuracy of the calibration is better than 1% at the
bright end (16-18 mag) over most of the survey area.
