The substrate temperature is one of the most important parameters for the synthesis of high quality diamond thin films in
hot filament chemical vapor deposition (HFCVD) system. Based on the principle of heat transfer, the substrate
temperature is calculated in the single hot filament system, the influence of filament height, filament diameter and
filament length on substrate temperature are also discussed. Results show that the substrate temperatures vary with the
space position. In the direction of parallel with the filament, the substrate temperatures vary smoothly, but, in the vertical
direction of the filament, the substrate temperatures change acutely. When H=8mm, L=7cm and df=0.5mm, the substrate
temperatures are well-distributed, this will give the support of some technique parameters for the growth of large area
HFCVD diamond thin films.