The heat transfer characteristics of allwelded plate economizer in different structure parameters and flue gas velocities were numerically simulated using Fluent and experimentally verified. The results show that the whole welding type plate heat exchanger whose major axis of the ellipse is 30 mm has the highest heat transfer coefficient, when the ratio of the shortlong shaft is 0.6, the flow path in interboard spacing of flue gas is controlled at 15 mm, and the rate of flue gas flowing is in 8 m?s-1. The highest heat transfer coefficient is about 50 W?(m2?K)-1.