Abstract: A novel technique was developed,for the first time to monitor in real-time the leakage of air into the high vacuum chamber of RF plasma enhanced chemical vapor deposition(RF-PECVD) reactor by analyzing the plasma emission spectrum with Real Time Plasma Spectrum Analyzer(RIPSA),comprising the spectrometer,USB device server,controller,optical fiber and monitor display.The influence of the gas medium with and without leaked air on the plasma emission spectra was investigated.The results show that the leaked air significantly affected the plasma emission spectrum,and that when it comes to leak detection of air with RIPSA,Ar-plasma outperforms H₂-plasma because of higher accuracy,bigger spectral difference and easier operation.We suggest that the rea-time leak monitoring/alarming with RIPSA may be of much technological interest in industrial fabrication of thin film transistors for liquid crystal display.