The evolution of the inner marginal radius r_(ms)of the black-hole accretion disk is investigated on the basis of general relativity. It is shown that r_(ms) is affected more strongly by the variation of black-hole angular momentum than that of blackhole mass during the whole evolution process from Schwarzschild black hole to extreme Kerr black hole. In addition,r_(ms) always decreases continuously and monotonously in this process. The range of values for the time derivative of r_(ms) is o...