Using YAG pulse laser ablation of a graphite target in vacuum chamber, laser plasma including carbon species can be produced, and a kind of carbon thin films can be formed on the silicon or quartz substrates. The possible radicals and their spatial distribution in the reaction chamber were probed by in situ optical emission spectroscopy of the laser plasma using optical multi-channel analyzer. The structure of the films was analyzed by Raman spectroscopy. It reveals that the films are diamond-like structure, and the atomic carbon and carbon ions are responsible for the formation of diamond-like structure of the films. The inlet of hydrogen in the reaction chamber much enhances the diamond component in the films. The spatial resolved optical emission spectroscopy indicates that there is a optimum position for the film formation in the reaction chamber.