Pressure Leak Calibration Apparatus is a metrology standard for calibrating gas leak rate and has been used to calibrate the pressure leak. Pressure leak is a kind of instrument, on the condition of defined temperature and inlet pressure (more than one atmosphere), to offer known leak rate to one atmosphere side. The pressure leak apparatus is composed of the system of constant volume method and the system of dynamic comparison method with quantitative gas. In the constant volume method, the pressure of constant volume is measured by absolute pressure method and differential pressure method, which both expends the lower limit and upper limit of measurement. In the dynamic comparison method with quantitative gas, the problem of verifying the unknown trace gas is solved with quantitative method. The sample of mixed gas and quantitative gas are produced with pressure reduction method and the gas introduced respectively into mass spectrum chamber with molecular flow method is analyzed by mass spectrum. With such technique, the repeatability is guaranteed. And the lower limit is expended for 2 orders and the small leak rate accordingly can be calibrated. The pressure leak can be calibrated with these two methods, respectively. In the multiple range of both the constant volume method and the dynamic comparison method with quantitative gas, there is satisfactory agreement. The range of constant volume method is from 1¡Á10@super 2@to 5¡Á10@super-3@PaL/s, uncertainty is from 2.6% to 9.1%£»the range of dynamic comparison method with quantitative gas is from 2¡Á10@super-2@ to 5¡Á10@super-5@Pa L/s, uncertainty less than 14.2%.