Abstract: The morphological structure of duck down and goose down was observed using optical microscope and scanning electron microscope. Explained quantificationally every parts size of down stone, down branch, down fibril and the node structure. Besides, studied the thermal properties of different down fiber and discussed the effects of the structure differences on fibers thermal property. Compared with the duck down, goose down possesses bigger down cluster, less down stone, longer down branch and finer down fibrils. The down fibrils distribute denser and the nodes arrange evener than duck down. The morphological structure gives the goose down better bulkiness and better thermal properties. The thermal property nonlinearly depended on the fiber volume fractions. With the increasing of the volume fraction, the thermal property of the fiber decreases firstly, and them improves. By the test verified, when the volume fractions are between 0.002-0.005, the fiber possesses the best heat retention.