Abstract:The experiments included many cycles from which the pore fluid pressures were different. Each cycle run under constant pore fluid pressure by increasing or decreasing confining pressure. Experimental data were dealt with by steady state method,and analyzed with response-surface method. It was found that the effect stress coefficient a varied with pore fluid pressure and confining pressure. At the higher confining pressures in the test,all of the coefficient a were below 0.11,which was contrary to conventional view. In order to analyze the stress-sensitivity of low-permeability sandstone sample,coefficient a = 1.0 and coefficient a obtained from the experiment were adopted. It was shown that permeability stress sensitivity was very strong as conventional a = 1.0 was used while hardly existed as the effective-stress coefficient a adopted from the experiment was used。