Abstract: Further research was conducted on the influence mechanism of graded or stepped porosity structures within porous media-filled positive-pressure standard leaks on leak rate under varying operating conditions. The article employed numerical simulation to establish a mathematical model. Analysis was performed on the effects of different graded and stepped porosity configurations, the outlet length ( \Delta x_2 ) of the positive-pressure standard leak, and different types of gases under varying inlet pressures on the leak rate. The pressure field distribution was also presented. The results indicate that under the same inlet pressure and temperature conditions, leak rates obtained with stepped porosity configurations are consistently higher than those obtained with either graded porosity or constant porosity configurations. For positive-pressure standard leaks with a graded porosity structure, the curvature of the pressure change curve increases with an increase in the absolute value of the gradient slope. The leak rate decreases as the outlet length \Delta x_2 increases.Under viscous flow conditions, the viscosity of the gas is inversely proportional to the leak rate of the positive-pressure standard leak. At an inlet pressure of 600 kPa, compared to a constant porosity of ε=0.2, a graded porosity configuration of ε=0.9−0.2 yielded an 86.4% increase in leak rate. Compared to the graded porosity configuration of ε=0.9−0.2, the graded porosity configuration ε=0.9−0.5 yielded a 179% increase in leak rate. The stepped porosity configurations ε=0.9−0.7−0.5−0.3−0.2 and ε=0.9−0.55−0.2 yielded increases in leak rate of 6.9% and 27.6%, respectively. Based on these findings, the study concludes that rationally designing the variation in the porosity structure of the porous medium can effectively control the leak rate and enhance its stability. This research provides valuable references for the manufacturing and design of positive-pressure standard leaks.