Abstract: According to water sensitive effect would cause a permeability failure to the coal reservoir, would reduce the permeability of the reservoir and thus would influence the production of the coalbed methane well, the physical features of the coal reservoir in Anze Block in the south part of Qinshui Basin and the water sensitivit y failure degree, the water sensitivity failure mechanism of the coal reservoir in the block was studied, and the scanning electron microscope observation, maceral, mat erial detection and water sensitivity test were conducted on the coal samples from No. 3 seam of Shanxi Formation in Anze Block. The test results showed that the wate r sensitivity failure rate of the coal samples from No. 3 seam in Anze Block was 29.92% ~ 54.03%, the average rate was 43.53% and the water sensitivity failure degree was between the weak sensitivity and the medium strong. The water sensitivity failure rate as well as the clay material content and the liquid flow velocity were in a posi tive correlation relationship and the water sensitivity failure rate and the coal and rock permeability were in a negative correlation relationship. There were two failure m echanisms existed in the coal reservoir water sensitivity effect. The first mechanism was that the water swelling of the clay material would cause a mechanism to reduc e the static permeability and the second was that the particle separated migration of the clay material would cause a mechanism to reduce the dynamic permeability.