Abstract: Through the self-developed pipeline testing system，the paper studies the critical conditions of jamming and the method of safety transportation under different velocity，particle size and concentration conditions of the pipeline testing system for coarse grains.The result shows that：①The particle size and concentration of coarse particles have important effects on the safety transportation system.With the increase of particle size and concentration，the critical velocity increased，and when the transportation velocity is greater than the critical velocity，it makes the transportation safe; ②At a certain particle size，the larger the inclination is，the lower critical velocity needed at pipeline jamming for coarse grains; ③In the case of pipe blockage，the critical conditions of the highly-efficient delivery for coarse grains depends on the concentration and velocity.

Key words: Coarse grain, Jamming, Safety transportation, Critical condition