In view of the unreasonable design of the dust filter mesh affecting the cooling effect of the transformer, a method for designing dust filter mesh width of transformer is proposed, which aims to reduce wind speed decay rate and dust filter weight, then establishes an optimal model on the basis of ensuring cooling effect of transformer, therefore the optimal value of mesh width for dust filter can be obtained. Based on the study of the structure of dust filter, the specific steps of the above method are displayed, and the optimal value of mesh width for dust filter is calculated for taking the cooler of 1 000 kV UHV transformer as an example. Finally, the wind speed decay rate test and field test verification have been done, which show that dust filter mesh width of transformer designed by this method can reduce the weight of dust filter, and be economical and practical on the basis of ensuring cooling effect of transformer, it verifies its validity and feasibility.