As a natural radioactive element, uranium and its compounds exist as aerosol and transfer in air. In gas phase, uranium can cause various kinds of radioactive damage to human body. The change in its concentration in a local area is related to the exploration and utilization of nuclear energy. Therefore, the development of field method for rapid uranium detection in air sample is very important. In this contribution, the air samples over uranium ores collected by a general pump was absorbed with 2.0 mol·L-1 nitrate and then reacted with solid reagent kit. When the reaction between trace uranium and chromogenic reagent was finished, the homemade portable photometer was used to measure the absorbance. The results showed that the concentration of uranium in air samples over low grade uranium ores can be successfully determined by the present method and the values agree with that obtained by ICP-MS. The RSD measured by the new method was 1.72%. The application of the new field spectrometry in discriminating uranium ores from other ores has the potential advantages of easy operation, cost-saving and high accuracy.