High quality optical grade thick diamond film wafers with different thickness are prepared by high power DC arc plasma jet CVD (DCPJ CVD) method using a CH4/Ar/H2 gas mixture. Three different powers, 13.65, 15.40 and 17.94kW, were employed during the investigation. The aim was to investigate the effect of these powers on the deposition of thick diamond film. The controlled system was discussed together. The results show that the average diamond grain size and growth rate increase with input plasma power, but a further increase in input power, diamond thick-film defects and amorphous carbon content increased.