With the development of high power microwave technology, the threat of strong electromagnetic radiation attacks on electronic devices is becoming more and more serious. Higher requirements are placed on the protection and reinforcement. Near-space vehicles and their discharge effect are less considered currently while lacking the corresponding test environmental conditions. A method of combining the near-space environment with the high power microwave is proposed. Experiment is conducted with strong electromagnetic zone in the cylindrical vacuum tank using the MW-level S-band microwave source and the radiation focusing system. The microwave source is adjustable in repetitive frequency 1-1000 Hz and pulse width 20 ns-20 μs. The atmospheric simulation chamber is adjustable under pressure 10-3-105 Pa and temperature -40 ℃ to 60 ℃ with effective volume over 4 m3. The center field intensity measured by small signal transmission is over 2 kV/cm. The experiment technology can be used to carry out the discharge breakdown research of near-space electronic system under high power microwave, which is helpful for the weak link analysis and protection reinforcement.