The invention relates to a photochemical steam generating-atomic spectrometry for determining trace iron, comprising the following steps of generating photochemical steam and detecting by introducing an atomic spectrometer. Different from the traditional method for pneumatic atomization and sample introduction, the spectrometry comprises the step of directly reacting formic acid and iron ions in a water solution under the radiation of ultraviolet light to generate the chemical steam (i.e. carbonyl iron) of the iron. The generated carbonyl iron is carried into the atomic spectrometer, an atomic fluorescence spectrophotometry (AFS) and an inductive coupling plasma-atomic emission spectrometer/mass spectrometer (ICP-AES/MS) for determination by carrier gas. The invention has the characteristics of sensitivity, economy, simplicity, safety, environmental protection, strong anti-jamming capability and the like.