Abstract: Asort of new rare earth color reagent-polyhalogenated bisazo chromotroplc acid derivants was designed and synthesized.They are easily soluble in water, alcohol and acetone, but insoluble in benzene, ethyl ether and chloroform.They are a kind of highly sensitive and excellently selective reagents for rare earth elements.The acidity of color reactions is strong (0.1N-4N) and the acidic range is wide.The relationship between the molecular structure and the reaction properties for rare earths was also studied.When the properties and positions of auxochromic groups are fixed, the sensitivities of reagents that have the complex functional groups-AsO₃H₂, -COOH and -PO₃H₂ are higher than others.