A method for acquiring an optimum position of a reserved block in a holographic storage system is provided. Firstly, an initial offset error between an initial reserved block and its two nearest neighbors is computed. Then, according to a dynamically adjustable modified centroid function β′, a second reserved block is obtained by interpolating the covariance values associated with the initial reserved block and the respective two nearest neighbors. Afterwards, the optimum position of the reserved block is acquired according to the second reserved block and the initial offset error.