in this talk, we give a mathematical derivation of a pathway- based mean-field model for e. coli chemotaxis based on the moment closure in kinetic theory. the pathway based model incorporate the most recent intracellular chemical dynamics. the derived moment system, under some assumptions, gets to the chemotaxis model pro- posed in [g. si, t. wu, q. quyang and y. tu, phys. rev. lett., 109 (2012), 048101], especially an important physical assumption made in which can be understood explicitly in this new moment system. we obtain the keller-segal limit by considering the moment system in the regime of long time and strong tumbling rate. numerical experiments are presented to show the agreement of the moment system with (individual based) signaling pathway- based e. coli chemotaxis simulator ([l. jiang, q. ouyang and y. tu, plos comput. biol., 6 (2010), e1000735]).