Spatially developing flow structure and mixing characteristics in turbulent jets issuing from three different nozzle geometries are investigated by using Reynolds Stress Models(RSM). In order to analyse the geometric effects on the flow mixing, round, square and equilateral triangular shape of nozzle exit plane are selected at a constant Reynolds number based on identical equivalent diameters. The variance of the mean velocity, streamwise vorticity, static pressure and turbulent intensity of square and equilateral triangular jet are compared with turbulent round jet. From the result, it is confirmed that the flow mixing of non-circular nozzle is enhanced by increasing the variance of streamwise vorticity and negative static pressure value. Equilateral triangular jet is the highest mixing efficiency among three different inlet nozzle geometries.