Pneumatic slug conveying in a horizontal straight pipeline is analyzed numerically. The gas flow is calculated by the method of characteristics, divided into three regions : 1, particle slugs; 2, particle free layers; and 3, particle settled layers. It is assumed that : (1) the shear stress on the surface of the settled layer is within a saltation limit; (2) the pressure drop through the particles obeys the Ergun equation; (3) the frictional force on the slug is due to the slug weight alone; (4) the height of the settled layer is constant; and (5) the voidage is constant. The particles are fed continuously into the pipe to form a slug. The feeding is stopped when the slug length exceeds a certain fixed value and generation of a slug is completed. Calculations are carried out for a constant gas mass flow rate under similar conditions to our previous experimental measurements.