We are concerned with the finite volume approximation for the Keller-Segel system,which describes the aggregation of slime moulds resulting from their chemotactic features.We study a linear finite-volume scheme satisfies both positivity and mass conservation properties.Under some assumptions on mesh,we establish error estimates in LP-norm with a suitable p > d,where d is the dimension of a spatial domain.We apply the analytical semi-group theory of the discrete Laplace operator to the error analysis.We derive the discrete version of Lyapunov functional for the finite volume solution,where the Lyapunov functional play important role in studying the global behavior of solution of Keller-Segel system.Some numerical experiments are performed to verity the theoretical results.