High-quality and large area nano-diamond film is prepared via double beam pulse laser irradiation of graphite suspension. The inhomogeneity of diamond films and influence of substrate temperature are improved. The microstructure and composition of the diamond films are detected by the visible Raman spectroscopy and higher solution transmission electron microscopy. The experimental result demonstrates that the Raman spectroscopy reveals that disorder peak is at 1334 cm-1 and graphite peak is at 1571 cm-1, the diamond film is compact and homogeneous, its average crystalline grains are around 5 nm. The composite beam provides moderate temperature for the growth of diamond films, and the continuous synthesis of homogeneous nano-diamond films is realized at normal temperatures and pressures.