The high stability and tightness of modern aviation hydraulic pipelines require them to have a very low leakage rate under variable pressure environments. Once the leakage of the hydraulic pipeline is likely to cause an irreversible air disaster. Flaring straight pipe joint is one of the most widely used in aircraft hydraulic pipelines. The establishment of the simulation model is an effective method to accurately predict the annular gap leakage of the pipe joint. The ring gap of the pipe joint is located inside the threaded sleeve, which cannot be directly observed. The existing leakage prediction methods usually only focus on the microscopic interface contact and ignore the leakage prediction of real complex structures. Therefore, this article is based on ideas, semi-physical simulation through experimental data calibration tightening torque and annular gap width and the mathematical relationship between void ratio, and then established the flaring type straight pipe joint circular aperture leakage prediction simulation model, the ability to different tightening torque and hydraulic pressure conditions for predicting the pipe joint leakage rate, finally, the simulation experiments have been carried out to verify prediction model, The validity of this method is proved.