A method and a power-saving control device for controlling operations of a plurality of computing units are provided. The method includes pre-estimating network service demands for the computing units within a next period. The method further includes: before the next period, calculating a first number and a second number of the computing units which are expected to be respectively in a busy state and a standby state within the next period according to the pre-estimated network service demands. The method further includes controlling the computing units such that the numbers of the computing units which are in the busy state and the standby state within the next period are respectively equal to the first number and the second number.