An improved semi-analytical correlation was proposed for the prediction of the flowfields downstream a typical swirl cup on the basis of previous correlations proposed by Rizk & Mongia. The improved correlation has clear physical definition and is adequate for its constants determination by large amount of experimental data. The comparison between the selected experimental data and the predictions by the correlation is quite well, especially about the characteristic data such as the peak velocity, the radial location of the peak velocity, the decay of the velocity, the size of the recirculation zone, and the development of the recirculation zone. Meanwhile, the influences of the constants in the correlation are shown quantitatively, and the possible reason has been analyzed briefly. The analysis showed that all the empirical constants were independent with each other, thus the semi-analytical correlation could be used easily as further validation for different data.