Abstract: In order to reasonably control coal fines output of coalbed methane （ＣＢＭ） well, taking high-rank coal in southern Qinshui basin as reseach object, permeability of fracturing fractures under different effective stress and different rate of water injection was measured. Based on the permeability, influence of coal fines output on permeability of fracturing fractures was discussed. The results show that with the increase of effective stress, permeability of fracturing fractures increases firstly and then decreases. When effective stress is equal to or less than 4 MPa, with the increase of effective stress, permeability of fracturing fractures declines rapidly because of the clogging of coal fines. When effective stress is more than 4 MPa, plastic deformation of coal matrix occurs, which causes the increase of permeability. When there is single grain size sand in fracturing fractures and the rate of water injection is equal to or less than 20 mL/min, the permeability declines rapidly because of the low water carrying capacity of coal fines and the serious clogging of coal fines. When rate of water injection is more than 20 mL/min, high velocity flow alleviates clogging of coal fines and the permeability has slowed down. When mixed sanding is in fracturing fractures, fracturing sand polishes the wall of fracturing fracture and causes the increase of permeability.