Based on the technology of using particles to block air-leakage fractures around drainage boreholes, pneumatic conveying experiments were conducted to explore the mechanism of particle deposition and blockage in fractures. Two small-size straight fractures (1000 mm x 40 mm x 2 mm and 1000 mm x 40 mm x 4 mm) were performed. The experimental results show that for the conditions under which fractures could not be blocked, average deposition height fluctuates around a certain value. This value is significantly influenced by air pressure but little impacted by mass flow rate. The average deposition height fluctuates sharply when solid flow rate increases. The effective blockage length curve slowly increases followed by a fast decrease. According to the effective blockage length, the optimum blockage effect is obtained at mass flow rate of 0.042 kg/s and air pressure of 0.25 MPa for a 2mm-wide fracture, while for a 4 mm-wide fracture, the optimum blockage effect is obtained at mass flow rate of 0.042 kg/s and air pressure of 0.15 MPa. Both air pressure and fracture width have approximately equivalent effects on the blockage time, whereas mass flow rate does not contribute a noticeable effect.