Abstract：A dynamic model of test system is established to study the seepage properties of non-Darcy flow in rock specimen，and seepage properties parameters(permeability，non-Darcy flow b factor，and acceleration coefficient) of limestone specimens are picked up based on the analysis of individual time series of porous pressure gradient. A new phenomenon comes to light in the test process that the non-Darcy flow b factor of the specimen in post-failure stage is less than zero. The discovery of this new phenomenon makes it possible for engineers to verify，forecast，and analyze the instability of seepage flow in rock in laboratory. Test results show that seepage flow in limestone does not obey Darcy¢s law whether it is in post-failure stage or in ante-failure stage. The permeability of non-Darcy flow is less than that of Darcy¢s flow when the non-Darcy flow b factor is positive；the seepage flow would be instable when the non-Darcy flow b factor is negative because of the interpenetration of fracture in the specimen. With the help of test results，the mechanism of water inrush in coal mines can be explained more convincingly by the nonlinear dynamics theory，and a new idea is provided to engineers in the control of water seepage in surrounding rock strata in coal mines. The tests adopt previously familiar methods，and more efforts are involved only in the data process. It does not increase the test cost，nor does it make the test more difficult. So it is doubtless to be used widely in the near future.
