Because the metal enclosure with apertures is the structure of the cavity form, FDTD method belonging to full-wave analytical algorithm isn¡¦t efficient for analyzing such case. Thereby the ETL method belonging to analytical formulation provides another way to analyze it. Although the structure which it can apply to isn¡¦t as complex as that in full-wave analytical algorithm, the computing time is shorter than FDTD. In contrast, the method can¡¦t get good agreement. Thus two improved ways are introduced in this paper. One is to make the suitable structure wider and the other is to consider the higher mode original ETL method isn¡¦t included to improve the accuracy. Further these two ways make the suitable range of the method wider and the method has good practicability.