Two kinds of poly (ethylene oxide) and poly (propylene oxide) diblock and triblock copolymers which have the same compositions but different block architecture have been synthesized in this work.The association properties of them were studied by fluorescence methods in aqueous solution.It was found that the copolymers with different block architecture have different properties.The triblock copolymer is easier to form micelles than the diblock copolymer in aqueous solution.But gelation is easier for the diblock copolymer than for the triblock copolymer.The results were explained and discussed preliminarily.