The plasma chemical vapor deposition is one of the most utilized techniques for the diamond growth. As the applications of diamond thin films prepared by plasma chemical vapor deposition(CVD) techniques become more demanding, improved fine-tuning and control of the process are required. The important parameters in diamond film deposition include the substrate temperature, $CH_4/H_2$ gas flow ratio, total, gas pressure, and gas excitation power. With the spectroscopic ellipsometry, the substrate temperature as well as the various parameters of the film can be determined without the physical contact and the destructiveness under the extreme environment associated with the diamond film deposition. It is introduced how the real-time spectroscopic ellipsometry is used and the data are analyzed with the view of getting the growth condition and the accompanied features for a good quality of diamond films. And it is determined the important parameters during the diamond film growth, which include the final sample will be measured with Raman spectroscopy to confirm the diamond component included in the film.