Abstract: Hot filament chemical vapor deposition (HFCVD ) is an useful technique to get high-quality diamond films with uniform thickness and in larger area. To explain the relation between geometry parameter of hot filament and the uniform of larger-area diamondfilm, a multi-filament and substrate heat exchange model was established. and both the irradiance and temperature fields were calculated. As it turned out that the uniform of diamond films is greatly determined by the irradiance field rather than the temperature field. Moreover, the suitable geometry parameters to prepare diamond films on 100 mm×100 mm area with HFCVD are given under such calculation.