In present study, a novel deposition method combining conventional hot filament chemical vapor deposition (HFCVD) method and surface polishing is adopted to deposit the micro/nano-crystalline multilayered ultra-smooth diamond (USCD) film on the cobalt cemented tungsten carbide (WC-Co) cutting inserts. The scanning electron microscopy (SEM) image shows that the deposited USCD film exhibits an ultra-smooth surface, whose surface roughness (Ra) is measured as ~95.7 nm using surface profilometer. The characterization of Raman spectroscopy and X-ray diffraction (XRD) further confirms that the grain size of USCD film is down to the nanometer scale. Furthermore, dry turning tests using Al/SiC-MMC as workpiece are conducted to examine the cutting performance of as-fabricated USCD coated inserts, comparing with uncoated WC-Co inserts, MCD and DLC coated inserts. The results show that the USCD coated insert exhibits much longer lifetime than other inserts, whose effective cutting length is as long as 190 m, nearly two times more than that of DLC and MCD coated inserts, and 5 times more than that of uncoated WC-Co inserts. The excellent wear resistance and ultra-smooth surface of USCD films is supposed to play determinate role on elongating the lifetime of WC-Co cutting insert.