The applicability of the three-dimensional vortex method to the analysis of jet is discussed through the vortex simulation of a compound round jet. For the vortex element, a blob model with finite core is employed, and the viscous effect is considered by using the core spreading method. The statistical properties are computed from the simulation. It is found that the core distribution function and longitudinal length of the calculating domain markedly affect the number of vortex elements and the flow field.