Abstract: The complex structure of double inlet gas flue has a significant influence on gas flow field distribution in a 1 000 MW coal-firedboiler′s low temperature economizer. In order to optimize gas flow field of the low temperature economizer with double inlet gas flues andensure the heat exchange efficiency and reduce its failure rate,based on the computational fluid dynamics(CFD) numerical simulationtechnology and the standardk-εmodel,the porous medium model was used to replace the fin heat exchanger with complex structure.Theflow field distribution in the low-temperature economizer and its double inlet flue of a 1 000 MW coal-fired unit is studied by numericalsimulation and structural optimization. In order to ensure that the simulation results were closer to actual situation,the numerical simula-tion model was verified by comparing measured values with calculated values of flue gas pressure loss at the corresponding sampling pointof low temperature economizer under different working conditions,then the reliable boundary parameters of the model were obtained.Thedeviation between the measured value and the pressure loss value corresponding to the numerical simulation before the optimization of thelow-temperature economizer flue structure was controlled at-23-31 PA,which verified the accuracy of the numerical model. After optimi-zing the structure of the low-temperature economizer and its flue,the established model was used to simulate the flow field. In differentboiler load conditions corresponding to the gas flue inlet velocity of 3.7,6.1,8.5,9.7,12.2 m/s,the numerical simulations had been maderespectively before and after optimizing structure of the low temperature economizer's inlet gas flue. The evaluation results show that gasflow field distribution in low temperature economizer has been worse and worse,when the velocity of flue gas at the flue inlet is more than5.3 m/s,before optimizing structure of the low temperature economizer's inlet gas flue and with the increase of boiler load,the air flowuniformity of the section becomes worse and with the increase of boiler load,the air flow uniformity of the section becomes worse.Afterstructural optimization,with the increase of flue gas velocity,the gas flow field distribution in low temperature economizer becomes worse,but within the excellent flow field distribution range(10%) and the uniformity of air flow distribution in the entrance section of the heat ex-change area is obviously improved.The results of numerical simulation show that the main reasons for uneven distribution of flow field ineconomizer and its inlet gas flues are unequal diameter of flue elbow and straight flue,unreasonable setting of guide plate and diffusion flueelbow. After making structural optimization of the low temperature economizer such as equalizing elbow to the straight flue diameter andsetting the guide plate reasonably,the gas flow deviation inside the vertical flue of the low-temperature economizer is obviously weakened,the air flow at the top of the elbow on the vertical flue is too small,and the air flow velocity at the bottom is too fast,so the air flow uniform-ity at the inlet of the heat exchange area of the low-temperature economizer is obviously improved. The analysis shows that the elbow withthe same diameter as the straight flue is beneficial to improve the uniformity of air distribution in the flue. When it is necessary to connectthe diffusion flue after the flue turns,the flue should be connected to the diffusion flue after a certain distance of equal diameter turning,which is conducive to improving the uniformity of air distribution in the flue.