Abstract: In order to ensure the secure and reliable operation of key pipe fittings in air cooling large exhaust pipelines of solar thermal power plants，ANSYS software is used to analyze a special reducing cross in the direct air cooling largediameter exhaust pipeline of 1×50 MW Xinjiang Hami Tower Solar Thermal Project. The stress state of the special reducing cross under the vacuum external pressure and self weight load is calculated，and its overall stability is analyzed. The stress calculation results are checked and verified according to the standard JB/T 4732—2005，which witness the necessity of improvement on the original pipe structure. The improved special reducing cross meets the requirements of the standard. The improvement can provide theoretical reference for the secure and reliable operation of a whole direct air cooling exhaust system.

Key words: direct air cooling, special reducing cross, finite element analysis, stress analysi, solar thermal power plants