A joint rate measurement method without Hongdan(Pb3O4) powder was proposed. The mechanical contact surfaces were simplified into the rough surface and the ideal plane. Through the establishment of contact deformation model, using the elastic contact theory, the formula for calculating the contact deformation was deduced, and then the joint rate of the contact surface was calculated. The test results show that the measurement method can be used to truly reflect the joint distribution of the mechanical contact surface. It provides basis for the sealing performance test of the tested model.