Three-dimensional structure of baroclinic wavy jet was experimentally studied in rotating annulus subject to a negative radial temperature gradient.General features of wavy surface jet in the system were obtained.Based on the precise measurements of velocity distribution of the jet with LDV and the three-dimensional temperature field in the convective system, three-dimensional thermodynamic structures of jet were gained, and by using a correlation of three-dimensional disturbed temperature, the unstable mechanism of disturbed temperature of baroclinic fluid in a rotating system was further discussed.