This paper has carried out the statistical and diagnostic analyses of development of cyclones in east sea area of China in spring from 2008 to 2014.Results show that the cyclones in east sea area of China in spring are shallow low-pressure systems.The vertical stretching height of the cyclones is below 600 hPa and the horizontal scale is less than 1 500 km.The strong weather with strong winds,big waves and heavy precipitation is mainly located in the southeast of the cyclone.The high wind jet region of cyclonic circulation of each level,which forms in the southeast of the cyclone,is called the cyclone jet.From the top to the lower,the jet axis of cyclone rotates counterclockwise in the vertical direction,which forms a funnel shape of cyclone with big top and small bottom.Cyclonic shear on the left side of cyclone jet is conducive to the maintenance of intensity of cyclone center,and the cyclonic shear on the left side of upper cyclone jets is correspond to the velocity convergence zone in the front of lower cyclone jets,which is beneficial for the cyclonic dynamic pumping and the strong vertical ascending motion in the southeast of the cyclone.The cyclone jets at different levels are configured to support the asymmetric structure of the cyclone and lead to the asymmetric distribution of cyclonic elements.Cyclone jet transports vertical helicity,horizontal helicity and sufficient water vapor into the cyclone and they are strongly lifted in the southeast of the cyclone,which enhances the release of condensation latent heat and prompts the development of cyclone and the strong weather area occurred in the southeast of the cyclone from thermal and dynamic aspects.The sea surface frontal temperature distribution in spring is beneficial to the enhancement of the cyclone jet,which reinforces the baroclinicity of the cyclone through non-adiabatic cooling in the northwest and non-adiabatic heating in the southeast of the cyclone.Environmenal westerly jet stream at high altitude is located in the right side of the cyclone,forming the whole deviation wind convergence,which effectively enhances the low level cyclone jet.Meanwhile,the momentum transports downward from the upper level and locates in the west side of the cyclone,leading to the development of weak current(i.e.the sinking branch of spiral structure of the cyclone) in the northwest of the cyclone,and then enhancing the spiral circulation of the whole cyclone,which makes the cyclone jet also begin to strengthen from the lower level.