Abstract: For HL tokamaks,a anthracene-acetone liquid fluorescent leak detection was developed for parts of liners,possessing a sensitivity of 10^-9 Pa·m³·s^-1 and a leak position resolving power of a better than 0.5 mm;a QMS was cooperated with a helium leak detector for high vacuum leak detection;a sniffer with a vacuum cover-helium leak detector set was developed for pressured vessels detection and some vacuum pumping sets suitable for pumping huge water vapor were developed also.In JET with a D-T plasma,a conventional helium leak detector（sector magnet type） is suffered severely interference,because the first walls retained D particles release D₂,and the released D₂（4.028 2 u） confuses the leaked ⁴He（4.002 6 u） due to the near identical masses.A selective pumping set,including a liquid nitrogen cooled trap to pump all condensable gases and a getter pump or a 10 K cryopump to pump off hydrogen and its isotopes,is in series at the entrance of the helium leak detector,and a compression pump for exammple,a molecular drag pump or a compound molecular pump is placed in front of the pumping system to enhance the sampling gas flow through it.The enhancements have made it possible to detects leaks at least three orders of magnitude smaller than previously practical.