The high quality germanium plays an important role in the field of information industry, national defense and aviation etc. CZ growth method is popular for crystal germanium production. For CZ growth method, the crystal diameter test is the basic function. Firstly the application of infrared diameter test device YPIR-QT during the crystal germanium growth is introduced, single crystal diameter is measured, the output signal acts as feedback signal of crystal diameter control system. Secondly the future intelligent improvements for infrared diameter test device YPIR-QT are suggested.