  Environment is one of the key external drivers of the galaxies, while active
galactic nucleus (AGN) is one of the key internal drivers. Both of them play
fundamental roles in regulating the formation and evolution of galaxies. We
explore the interrelationship between environment and AGN in SDSS. At a given
stellar mass, the specific star formation rate distribution of the AGN host
galaxies remains unchanged with over-density, with the peak of the distribution
around the Green Valley. We show that, at a given stellar mass, the AGN
fraction that has been commonly used in previous studies (defined as the number
of AGNs relative to all galaxies including passive and star forming ones) does
decrease with increasing over-density for satellites. This is largely due to
the fact that the fraction of passive galaxies strongly depends on environment.
In order to investigate the intrinsic correlation between AGN and environment,
especially under the assumption that AGN feedback is responsible for star
formation quenching, the AGN fraction should be defined as the number of AGNs
relative to the star-forming galaxies only. With the new definition, we find
little dependence of AGN fraction on over-density, central/satellite, and group
halo mass. There is only marginal evidence that AGN may prefer denser regions,
which is possibly due to more frequent interaction of galaxies or higher merger
rate in groups. Our results support the scenario that internal secular
evolution is the predominant mechanism of triggering AGN activity, while
external environment related processes only play a minor role.
