To study the regulation property and opening behavior of a regulatable dry gas seal (RDGS),based on gas lubricated theory,a numerical model for a RDGS was set up by introducing into the parameter of regulation ratio of pressure and equilibrium film thickness was set as the regulatable target.Reynolds equation was resolved by using finite element method,and the effect on seal performances by varying regulation ratio was studied under the actual working conditions.With the hypothesis of critical gas film thickness,a criterion for expressing the opening behavior of RDGS,namely the compound opening ratio,was proposed.The results show that the seal performances of RDGS can be stabilized in a scope by varying the regulation ratio,but the scope varies with the working conditions.The regulation property of pumpingin dry gas seal (PiDGS) is better than that of pumpingout dry gas seal (PoDGS),while the opening characteristic is on the contrary.The theoretical results of this method are verified by experiments,it provides a method for analyzing the opening behavior of RDGS.