Diamond thick films are fabricated by hot filament chemical vapor deposition(HFCVD).The distance between filaments and enclosure are investigated to obtain high quality diamond thick films.By changing the distance between filaments and setting up enclosure,the growth rate can be up to 7.5 μm/h,and the thermal conductivity can be 1028 W/(m·K).The diamond films have dense structure and even let the red light through.