Abstract: The conductance of some vacuum valve or orifice needs to be measured in vacuum system,.A new method for measuring orifice molecular flow conductance by increasing pressure is put forward.The measuring formula is given.The relative combined standard uncertainty of the orifice conductance is given by evaluation.In addition,the results are validated by the conductance of same orifice measured by the method of linear vacuum gauge.It was found that the increasing pressure method is sample,convenient and quick for conductance measurement.