Abstract: An electron assisted chemical vapor deposition (EA-CVD) method was used to synthesize a uniform diamond thick film. The factors that influence the uniformity of quality and thickness of diamond thick films are methane concentration, gas pressure, bias current and the distance between filament and substrate. Results show that state of the glow discharge plasma plays an important role in the uniformity of quality and thickness of the diamond films. A larger filament-substrate distance, bigger bias current and lower gas pressure in the reactor can improve the state of the glow discharge plasma, resulting in an optimized uniform diamond thick film with diameter of 80mm, thickness of 1mm, and with a non-uniformity of thickness and thermal conductivity less than 5% and 10%, respectively. The abrasiveness ratio, defined by the abrasive weight loss of a standard grinding wheel divided by the abrasive weight loss of the resultant diamond film, is about 1.5×105, which is same in the middle and edge of the sample.