High quality diamond films were successfully prerared on quartz via the radio frequency plasma enhanced hot filament chemical vapor deposition(RF HFCVD)process. The effects of substrate temperature, reaction gas pressure and RF power on the structural and optical properties of prepared films were studied. The results show that their optimal values are 700℃, 2×133Pa and 200W, respectively. Under the optimal deposition parameters, the achieved diamond nucleation density can be as high as 10 11 cm -2 , and after growth for 1 h, nanocrystalline diamond film can always be obtained with its grain size of about 25nm, its average surface roughness of about 55?, and its optical transmission of 90% in the infrared region(800nm).