The estimation on the blockage boundary condition is significantly important for dense-phase pneumatic conveying of particles through bending slits. This paper presented the blockage characteristics for dense-phase pneumatic conveying in a bending slit. The bending slits with different bending angles were established, and the blockage boundary conditions were investigated in detail. The results show that the critical solid loading ratio for blockage initially decreases with the increase of superficial air velocity with different conveying pressures and bending angles of the slits, which agree with the existing studies and the current theories. Furthermore, it was found that there exist a minimum solid loading ratio, and when superficial air velocity is greater than that of the minimum solid loading ratio, the solid loading ratio actually begins to increase with the increase of air velocity. Meanwhile, with the increasing of the bending angle and the conveying pressure, the critical solid loading ratio increases, and the minimum solid loading ratio for blockage also increases. Therefore, the efficient and economical blockage of slits could be obtained by adopting the minimum solid loading ratio and its corresponding superficial air velocity. (C) 2014 Elsevier B.V. All rights reserved.