Abstract: The group 4 coal seam in the Dafosi mine filed belongs to the low rank coal, and the coal reservoir has good physical properties and abundant CBM resources, however, the gas production of the vertical wells is rather different. Based on the characteristics of coal reservoir parameters and the practice of CBM ground development, fuzzy mathematics was used to set up the membership function of reservoir parameters of 4 vertical CBM wells with the same engineering parameters and a big difference in production. Reservoir has been evaluated and the result was consistent with actual production. Specifically, reservoirs uncovered by wells DFS-133 and DFS-45 are conducive to development, reservoirs penetrated by wells DFS-69 and DFS-105 are not. After comprehensive assessment of reservoirs of seam group 4 in 4 vertical CBM wells, it can be concluded that resource, preservation and development factors are influence factors of productions of the vertical wells with same strengthening measures. The conclusion has significant meaning for CBM development and selection of favorable area of upper seam 4.