Abstract: The mechanism of tin atom formation lin a pyrolytic Zr-coated and ordinary graphite furnace atomizer is studied. The gas phase molecular absorption spectrum of SnO is measured. X-ray diffraction technique is used to determine the state of the compounds on the inner surface of the tube. It is suggested that, in ordinary tube, the tin atom is formed mainly through the thermal dissociation of SnO, while in the pyrolytic Zr-coated graphite tube, ZrC reduces SnO or SnO_2 to Sn, which is then atomized through vaporization.