On the basis of the forces on the differential element in the solids bed, a function between bulk density and pressure, and the nonisotropic pressure distribution in the element, an expression of pressure in the circumferential direction is derived. And the total power introduced through the positive conveying and the friction dragging conveying is also deduced. Experimental data are obtained using a self-developed and simplified vane extruder with an adjustable rotor eccentricity. The solids conveying mechanism in the solids compaction zone of a vane extruder is theoretically and semiempirically confirmed. Besides, the various portions of total power consumption including the power dissipated on the surfaces of the stator and baffles, the power used to build pressure and the power converted into rotational kinetic energy are derived. The effects of the eccentricity on the solids conveying are also discussed theoretically and semiempirically. POLYM. ENG. SCI., 55:719-728, 2015. (c) 2014 Society of Plastics Engineers