Mo thin films were fabricated on Si(100) substrates using a pulsed laser deposition (PLD) technique. The relation between crystallinity of films and laser fluence was investigated; the growth mechanism of films and the action of particle energy on the film growth were discussed. The AFM images show that the Mo films are flat and smooth, whose RMS (root-mean-square) roughness is less than 2 nm. XRD results show that with the laser fluence increasing, diffraction peaks of Mo films become narrow and surface roughness rises. Furthermore, Mo films convert into polycrystal state from amorphous state, and the grain sizes increase gradually.