Abstract: The influence of the structural factors (the type of complcxing agents, the kind and the number of bonding atoms and their relative position, the conjugated system and its size, the formation of chelate ring and the molecule with or without sulfonic acid group) of organic complexing agents on the enhancement effect of ytterbium was studied in an air-acetylene flame. The rule and the mechanism of the enhancement effect were discussed. The results indicate that the kind of bonding atom is a important factor deciding enhancement OT suppression action of complex-ing agent and the information obtained should be a comprehensive result affected by all these factors cooperatively in this case.