The invention relates to an asynchronous roller alternating control method for band steel hot rolling downstream rack working rollers. After a rolled piece is rolled, upper and lower working rollers horizontally move at the same distance in an opposite direction, then a next rolled piece is rolled, and the upper and lower working rollers periodically alternate to and fro between forward and reverse maximum roller alternating stroke positions in a band steel rolling production process, so that phasic positive and negative deviation is respectively performed on previous three downstream racks onthe basis of the same roller alternating function, and asynchronous roller alternation is formed on the three racks. According to the roller alternating control method, on one hand, the control ability on wedge and deviation is increased through asynchronous phasic adjustment, and on the other hand, the bad influence caused by multi-rack roller alternating zero-position superposition in the wholeroller alternating cycle can be avoided, so that the control stability of all strip-shape indices is increased, and the rolling kilometer is extended.