The invention relates to the field of production and control of a finish-rolled band steel, in particular to a method for controlling a thickness of a finish-rolled band steel. An adaptive control method for increasing the thickness precision of a finish-rolled steel band by utilizing a roll gap is characterized in that the method comprises the following steps of establishing a roll gap modification quantity static table which performs indexing according to the layers of band steels; before rolling the band steels, identifying the layer of the current rolling band steel, determining the roll gap modification current value, summing the roll gap modification current value with the zero point modification current values of racks, obtaining a roll gap model learning coefficients of the racks used for rolling setting pre-calculation; after rolling the band steels, detecting the obtained band steel final rolling thickness value and the actual roll gap value of the rack at the finish-rollingend, calculating the values, obtaining the band steel final rolling thickness deviation, the initial roll gap deviation value and the roll gap modification update value, for example, when the layer of the same coil of band steel is different with that of the former coil of band steel, the roll gap modification update value is saved in the roll gap modification quantity static table; and collecting the roller speed, roll gap, rolling force and final rolling thickness actually measured data of each rack, and then performing zero point modification of the roll gap. According to the method provided by the invention, the roll gap modification value and zero point modification are used jointly, so that the adaptive capability of the roll gap model under the condition that the rolling planning specification is variable can be improved, thereby improving the setting precision of the model and realizing accurate control to the thickness of the band steel.