Abstract: ZnSe:Co thin films were deposited on sapphire substrates at various ambient pressures by pulsed laser deposition. The influence of pressure on the propagation of plume, microstructure, surface morphology, and optical properties of films were investigated in this experiment. With the increase of ambient pressure, the propagation distance of the plasma plume decreased, the deposition type transformed from sputter to adsorption, and then the crystalline quality was promoted substantially. The optical band gap decreases with increasing deposition pressure, which may be associated with the quantum confinement effect. Excellent crystalline quality and (111) preferred oriented thin film was grown at the pressure of 10 Pa.