The invention provides a high-accuracy control method and system for a feedforward thickness of a cold-rolling mill. The high-accuracy control method comprises the following steps: calculating a feedforward AGC control quantity according to an inlet thickness difference mean value of strip steel, and carrying out dynamic averaging to obtain a dynamic average value of the feedforward AGC control quantity; carrying out a pressing speed test to acquire the relationship between a pressing speed of a hydraulic pressing system and a rolling force; acquiring a pressing speed corresponding to a set value of the pass rolling force according to the relationship between the pressing speed and the rolling force, and then calculating a feedforward AGC lead time according to the dynamic average value ofthe feedforward AGC control quantity; and evaluating a sampling time value corresponding to the feedforward AGC lead time, and transmitting the feedforward AGC control quantity through a modified synchronous transmission model. According to the high-accuracy control method and system, the feedforward AGC lead time is dynamically estimated, and the control quantity is applied onto the strip steelat a proper time, so that the problem that feedforward AGC cannot be easily executed at a proper time, is solved, performance deterioration caused due to a wrong execution time is avoided, the purposeof eliminating the inlet thickness difference of the strip steel is achieved, and the practicability of feedforward AGC is greatly improved.