Aiming at the problem that it is difficult to quantitatively detect the leakage pore size of pressure gas pipelines, a method for estimating pore size equivalent based on characteristic function is proposed. This method studies the data characteristics of the micro-hole leakage noise of the pressure gas pipeline under constant pressure and temperature conditions as the leakage signal source in the 40kHz ultrasonic frequency band, and extracts the characteristic parameters of the leakage signal in the time domain and frequency domain ,established the functional relationship between each characteristic parameter and the leakage aperture, and selected the optimal characteristic function through error analysis,Combined with MATLAB signal processing, the aperture size of micro-leakage is estimated. The experimental results show that the Hilbert relative energy of the leakage signal and the aperture size are fitted to the characteristic function of the third order, and the error between the estimated value of the leakage aperture and the actual value of the leakage aperture is within 0.05mm. The purpose of the study on the estimation of the leakage aperture equivalent is provided, and It can be used for reference in quantitative analysis of the equivalent of micro leakage holes in gas pipelines.