. High quality 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. The effect of substrate temperature on the quality of diamond film was studied with theoretical analysis and experimental investigation. The results indicate that different structures in diamond film may grow with different substrate temperatures. The temperatures of 800°C, 900°C and 1000°C were tested in the experiments. The quality of diamond film showed the best at the temperature of 900°C. Characterization by X-ray diffraction, Raman spectroscopy and SEM analysis are also carried out.