Abstract: A method for assessing and improving the performance of a finned tube heat exchanger under non-uniform face velocity is disclosed. First, a mathematical analysis method of the finned tube heat exchanger under the non-uniform face velocity is established. Second, a heat exchange amount and the heat resistance of the heat exchanger are obtained. Third, a quantitative relation between the non-uniform face velocity distribution and the performance of the finned tube heat exchanger are obtained. Finally, the heat exchange amount and the heat resistance of the heat exchanger are drawn in a rectangular plane coordinate system; and the coordinate system is partitioned in accordance with change rules of the curves, so that a performance assessment diagram of the finned tube heat exchanger under the non-uniform face velocity condition is obtained.