Since the end of the 20th century, jellyfish Cyanea nozakii Kishinouye bloomed in Northeastern China Sea, the Yellow Sea and the Bohai Sea, and there was tendency for increasing intensity. They have led to the broken net and influenced the fishing season of the East China Sea, the Yellow Sea and the Bohai Sea. The main purpose of this study was to provide taxonomic evidence when investigations of Cyanea nozakii in natural fields were carried out for the forecast of jellyfish blooming. In this paper, morphology of different developmental stages of the scyphozoan Cyanea nozakii was described particularly from fertilizedegg to adult medusa stages. The fertilized eggs develop into a ciliated planulae which form into planoconvex cysts (planulocysis) on attachment prior to forming a polyp. Elongation of the barrowing stalk occurs in the early excystment, flaskshaped in outline gradually becomes newly metamorphosed scyphistoma with four tentacles. They reproduce asexually by two ways including podocyst and stolon. Strobilation is typically monodiscous. Newly liberated ephyra have 8 marginal lobes, 8 rhopalia and 8 pairs of bluntshaped lappets, aberrant specimens with maximum 12 and minimum 6 marginal lobes. In the mean time, morphological difference between ephyra of Cyanea nozakii and ephyra of Rhopilema esculentum are compared. Adult medusa of Cyanea nozakii are about 200-300 mm, maximum size of over 500 mm. Middle of smooth exumbrella is marked by a lot of scattered nematocyst batteries. They have 8 marginal lobes, 8 rhopalia, strong oral canalis carpi, and a lot of long tentacles. By the c haracters of tentacular pouches is connected with sense gastric pouches on the fringe of the umbrella by transverse tube, and peripheral canals with numerous anastomoses, Cyanea nozakii would be distinguished from Cyanea capil lata, Cyanea ferruginea and Cyanea purpurea.