Abstract: We used hot filament chemical vapor deposition method to synthesize fine grain diamond films on silicon wafers aiming to exploit diamond's acoustic properties. The smaller grain size is contributed to achieving lower propagation loss. There are some important factors that can control the grain size such as gas pressure, the concentration of argon and methane and substrate temperature. In order to investigate how the factors have effect on the growth of fine grain, we measured the diamond film samples that deposited in different conditions through SEM and Raman spectrum. The results show that in the range of Iow pressure (below 2000Pa), with the gas pressure lower, the concentration of methane decreases. So in that way we can grow the uniform quality diamond films and the non-diamond component carbon (such as graphite and amorphous carbon) can be restrained. When the gas pressure reach some level, the grain size turns into fine and even is in the nanometer range.