In order to calculate the optimal adjustment amount of flatness actuators of rolling machine fast and precisely, and to minimize the online flatness error of the strip, a flatness control method, namely the matrix analysis method, which was based on the shape control efficacy, was put forward. The matrix analysis method converted the multi- variable optimal function into the standard quadratic function, calculated the minimum absolute value of the m variables in the corresponding feasible region respectively, and then optimal adjustment amount was obtained through the matrix inversion; after all, the best adjustment amount of flatness actuators in the feasible region was gained. In order to verify the correctness of the matrix analysis method, the least squares method and matrix analysis method were used respectively to accurate the best adjustment of 1450 tandem cold rolling system. As the results show, compared with the least squares method in the case that some actuators outputs are saturation, matrix analysis method obtains a second global optimal solution, so optimal control of the system can be achieved.