Friction and wear behavior of fine-grained diamond (FGD) films were investigated in the ambient air, deionized water and paraffin oil lubricating environment. The FGD films were deposited on WC substrates using HFCVD method and the tribologcial tests were conducted in a ball-on-plate type reciprocating friction tester where the mating balls were made of ball-bearing steel. Scanning electron microscopy (SEM), surface profilometer and Raman spectrascropy were used to study the characterizations of the deposited FGD films, and after sliding tests, the worn areas on both mating balls and FGD films were investigated and the wear debris layer adhered to the friction area of FGD films were analyzed with EDX. The experiment results suggested that FGD films exhibited steady friction coefficient as about 0.25 in water, lower than that in open air, which is up to 0.40; but the mating ball in water suffered much severer wear lost and its specific wear rate was more than two times higher than that in air, up to 3.6E-4 mm3N-1m-1. As while, a thick and compact layer of wear debris was observed on the worn area of FGD films sliding with water lubrication while only little debris existed in the diamond grain boundaries, which might dominate the friction process and attribute to the lower friction coefficient and higher specific wear rate in water environment. In oil environment, furthermore, both the friction coefficient and specific wear rate reached minimum value as low as 0.1 and 1.1E-4 mm3N-1m-1, no observable wear scar could be measured on the sliding surface of the FGD film.