In this paper , we present a multi-color photometric study of the nearby spiral galaxy M81 , using images obtained with the Beijing Astronomical Observatory 60 / 90 cm Schmidt Telescope in 13 intermediate-band filters from 3800 to 10000Å .
The observations cover the whole area of M81 with a total integration of 51 hours from February 1995 to February 1997 .
This provides a multi-color map of M81 in pixels of 1 \arcsec . 7 \times 1 \arcsec . 7 .
Using theoretical stellar population synthesis models , we demonstrate that some BATC colors and color indices can be used to disentangle the age and metallicity effect .
We compare in detail the observed properties of M81 with the predictions from population synthesis models and quantify the relative chemical abundance , age and reddening distributions for different components of M81 .
We find that the metallicity of M81 is about Z = 0.03 with no significant difference over the whole galaxy .
In contrast , an age gradient is found between stellar populations of the central regions and of the bulge and disk regions of M81 : the stellar population in its central regions is older than 8 Gyr while the disk stars are considerably younger , \sim 2 Gyr .
We also give the reddening distribution in M81 .
Some dust lanes are found in the galaxy bulge region and the reddening in the outer disk is higher than that in the central regions .