Abstract: With consideration of side-wall stability, sand production, toolstring safety and other problems, only the upper limits of differential pressure are reviewed during formation test. In fact, invading solids in formations may not be discharged effectively at low testing differential pressure. With consideration of the minimum differential pressure required for discharging invading solids, the model for lower limits of differential pressure for testing low-porosity and low-permeability gas reservoir was constructed to take dragging forces required for discharging invading solids and seepage characteristics of low-porosity and low-permeability gas reservoirs into account. Invading solids can be effectively discharged, together with higher productivities and more accurate formation data can be measured at differential pressure higher than that calculated using the newly developed model. Field application results show the model can satisfactorily determine the testing differential pressure required for field operation and provide necessary references for designing the pressure .