Abstract: Under full-filling conditions,the motion form of bulk materials in horizontal pipe screw conveyor is complex and completely different from that of ordinary screw conveyor.In this study,bulk mechanics theory was applied to analyze the mechanical condition of materials in the machine,the complicated force was simplified reasonably for establishing mechanical model,and the force and direction angle from the spiral blade were calculated by calculus.The results showed that the movement direction of bulk materials in horizontal pipe screw conveyor could be calculated under full-filling conditions according to the size of the screw blade,the friction coefficient of the screw blade and the size of the machine barrel.And then,the calculation formulas of axial movement speed and flow of materials were further derived.Finally,the final calculation formula was determined by comparing the calculated value of flow with the measured value.