The evolution characters of angular velocity Ωh of central black holes of accretion disks (including thin and thick disks) are investigated by considering both accretion and the Blandford-Znajek (BZ) process. It is shown that the rate of change of Ωh with respect to time truns from the positive value to the negative, as the dimensionless angular momentum a* evolves to a critical value. Evolving in a non-monotonous way, Ωh increases at first, and then decreases in a prograde accretion process. Therefore there exists a maximum of Ωh. It is pointed out that dimensionless angular momentum a* is more appropriate to describe the spinning state of a central black hole of an accretion disk than angular momentum J and angular velocity Ωh.