The ultrastructure of vitellogenesis was observed by the transmission electron microscopy in Hucho taimen at different developmental stages. The results indicated that the yolk of H.taimen was concentrated mainly at primary oocyte phase. On the basis of the composition and accumulation of yolk and change of organelle participating in the formation of the vitellus granule in oocyte, the vitellogenesis was divided into four phases: Provitellogenic stage, vitelline vacuole stage, vitelline accumulation stage, vitelline accumulation completion stage. The provitellogenic stage refers to the period before the yolk material begins to accumulate in the process of oocyte development. During this period, the nucleolus disintegrated unceasingly and clusters of mitochondria appeared, meanwhile, three layers of functional membrane structure formed outside the oocyte. The organelle changed unceasingly, yolk vacuoles and cortical vesicles generated at the vitelline vacuole stage. At the vitelline accumulation stage, the membrane of follicle was made up of zona radiata, granular cells layer, basement layer and sheath cell layer in order while the exogenous yolk material accumulated in sheath cell layer through blood flow, then went through basement layer by micro-pinocytosis, and finally reached granulosa cells by multivesicular body action, where yolk protein particles formed by processing and modification of the protein. The yolk protein particles went through zona radiata by micropinocytosis and aggregated into the vacuoles that formed at the periphery of oocyte and accumulated to from yolk globules. At the vitelline accumulation completion stage, the volume of yolk globules that assembled to the center of cell was increased and a majority of the oocyte was full of yolk globules, and the yolk accumulation was accomplished.