Pure ZnO and 5at%, 7at%, 9at% Sn - doped ZnO materials are prepared by the chemical co - precipitation method. They were annealed by furnace at temperature range of 300 - 700ºC in air for 1h. The ZnO materials are characterized by X - ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the Sn - doped ZnO materials appear rough porous structures. The maximum sensitivity can be achieved by doping the amount of 7 at%. It has much better sensing performance towards ethanol vapor under visible light irradiation. The response and recovery time are ~1s and ~5s, respectively. The mechanism for the improvement in the sensing properties can be explained with the surface adsorption theory and the photoactivation theory.