  In this paper, we study the idea about gravity as entropic force proposed by
Verlinde. By applying the identification between partition functions of gravity
theory and the dual field theory, we find the gravitational force can be
calculated from the changing of entropy induced from its dual field theory
side. Unlike Verlinde's calculation, our method does not depend on other
assumptions such as equipartition of energy, so it is a safe check on the
entropic force idea. Also we show how entropic force can be derived by similar
method from gravity side along, which will provide a clue to a better
understanding on the gauge/gravity duality. At last, we study the fluctuation
of the force, and we find the fluctuation acting on the point-like particle can
never be larger than the expectation value of the force. For black hole in AdS
space, by gauge/gravity duality, the fluctuation is induced by thermal
fluctuation from field theory living on conformal boundary. And for the metric
of black hole in flat space, the ratio between fluctuation and force goes to a
constant$\frac{T}{m}$ at infinity. .
