We have developed a novel scaling-parameter-dependent subthreshold swing model. By considering the effective conducting path effect (ECPE), this model generalizes the previous subthreshold swing model and precisely predicts the subthreshold swing for DG SOI MOSFETs without considering quantum effects. The model shows that the subthreshold swing could depend only on a scaling device parameter (α3). The calculated subthreshold swing S matches well with the simulated results by MEDICI. Our model is simple and offers an efficient scaling rule for DG SOI MOSFETs.