Abstract: It is the purpose of this paper to review new developments on the binary and ternary synergism of uranium ( VI ) which have been studied by us since 1982. We adopt Xu Guangxian's classification proposed in 1963 of the various synergic systems, namely: (1) ABC type-Acidic plus neutral andcationic extractants. (2) AAB type-Two acidic plus neutral extractants. (3) ABB type-Acidicplus two neutral extractants. (4) AAC type-Two acidic plus cationic extractants. ( 5) ACCtype-Acidic plus two cationic extractants. (6) BBC type-Two neutral plus cationic extractants.(7) BCC type-Neutral plus two cationic extractants.The stoichiometry of the synergic extraction adducts deduced by slope analysis,equal molar series method,Karl Fischer titration of the water content and calorimetric techniques are discussed.The mechanism of synergic extraction derived from a variety of principles is described with special emphasis on uranium ( VI ) which has been thoroughly investigated. According to our opinion, the synergic effect of chelate, ion association and neutral extractants in ternary system arises from satisfying the electricity neutrality principle, loss-of -hydrophilic principle,minimum charge density principle,coordination saturation principle, packing saturation principle and coordinate substitution principle. Among these principles the minimum charge density principle may play a dominant role in AAC and ABC systems ; the coordination saturation principle in AAB type and coordinate substitution principle in ABB type reaction mechanism etc."Coordinate saturation" is widely used in extraction mechanism, but it is a critical problem with actinide compounds considering the weak ligand field interactions of f-electron. It is suggested in the recently developed ligand packing model that on certain stage of packing, more ligands would be prevented to approach the coordination sphere, because the weak energy decrease due to crystal field stabilization is unable to compensate the energy increase due to ligand repulsion. An equilibrium should exist between bonding and steric repulsion. The cone packing model applied in synergic extraction of uranium ( VI ) is introduced in this paper.