  We employ the corrected Gaia Early Data Release 3 (EDR3) photometric data and
spectroscopic data from the Large Sky Area Multi-Object Fiber Spectroscopic
Telescope (LAMOST) DR7 to assemble a sample of approximately 0.25 million FGK
dwarf photometric standard stars for the 12 J-PLUS filters using the Stellar
Color Regression (SCR) method. We then independently validated the J-PLUS DR3
photometry, and uncovered significant systematic errors: up to 15 mmag in the
results of Stellar Locus (SL) method, and up to 10 mmag mainly caused by
magnitude-, color-, and extinction-dependent errors of the Gaia XP spectra with
the Gaia BP/RP (XP) Synthetic Photometry (XPSP) method. We have also further
developed the XPSP method using the corrected Gaia XP spectra by Huang et al.
(2023) and applied it to the J-PLUS DR3 photometry. This resulted in an
agreement of 1-5 mmag with the SCR method, and a two-fold improvement in the
J-PLUS zero-point precision. Finally, the zero-point calibration for around 91%
of the tiles within the LAMOST observation footprint is determined through the
SCR method, with the remaining approximately 9% of tiles outside this footprint
relying on the improved XPSP method. The re-calibrated J-PLUS DR3 photometric
data establishes a solid data foundation for conducting research that depends
on high-precision photometric calibration.
