Abstract: In order to solve some problems existing in the helium pressure leak detection technology of the pseudo-sealed source and clarify the calculation formula and test method, the paper deduces the helium pressure leak detection formula of the pseudo-sealed source by using the calculation formula of leakage rate and temperature, sample size and, and high and low pressure on both sides of the leak hole under the state of molecular flow. Through the research of the derived formula, it shows the actual standard leakage rate L is characterized by double value when the indicating leakage rate R is used to calculate the actual standard leakage rate L. It is necessary to carry out crude leakage detection after fine leakage detection to eliminate the existence of large leakage holes; The calculation formula given by GB/T15849 is the simplified formula of helium pressure leak detection formula under certain conditions (t₁ and t₂\ll P₀V/L). Direct use will magnify the rejection point and lead to misjuded results. In this paper, the influence of pressure, pressure time and purification time on rejection points under different cavity volume and qualified leakage rate has been discussed. The results show that increasing the pressurization pressure, prolonging the pressurization time and shortening the purification time can improve the indicating helium leakage rate R, so as to improve the leak detection sensitivity. When the influence of purification time is small, the pressurization pressure and time should meet P_Et₁≥QP₀²V/L². and the selection principle of helium pressure test conditions is provided.