A parameterized 3-D finite element model of the screw conveyor of a decanter centrifuge was established. With the model, stress analyses for the screw conveyor under normal operation conditions were carried out and the influences of the structural parameters were investigated. Orthogonal designs were used to sort out major factors and optimize calculations for the effects of factors on the strength of the conveyor. With the finite element calculation results, four empirical formulas for the strength of the conveyor under different loadings were regressed. By applying stress superposition principle, strength check criteria under normal operation conditions were given which can be used for the design of the screw conveyor.