Abstract: The technical measures and the main principle of the European Space Agency leak detector are used for reference.The high vacuum system of mechanical pump and molecular pump is used to get high vacuum.The titanium sublimation pump is designed to hold high vacuum.The high sensitive quadrupole mass spectrometer analyzes the multi search inert gases.The leak detector principle,design character and design calculation are introduced in the paper.The many experiments show that the leak detection limit under the air environment for CF 4 and He is 5×10 -8 ,while the limit for Ne is 5×10 -7 .