The fabrication of a diamond near infrared antireflective filter window and its application in industry are discussed. Using hot filament chemical vapor deposition (HFCVD) method, a diamond near infrared antireflective filter window (model DIFW-1, working wavelength was 1.3～1.8 μm) was successfully fabricated. The detector with the diamond window DIFW-1 has been successfully used in on-line monitoring at Shanghai Baosteel Works. It is sensitive and reliable, and working very well in the high temperature corrosive environment.