Parshall flume is more practical one of hydraulic structures for measuring flowrate in open channels and also has more advantages when the magnitude of flow velocity is relatively lower or much more sediments are brought from upstream. International Organization for Standardization (ISO) has suggested the empirical formulas standardized by the sizes and dimensions of Parshall flume. However, the related studies using the numerical simulations and experiments are relatively rare. Therefore, in this study, it was examined whether the numerical simulation was adequacy for reproducing the hydraulic characteristics of Parshall flume as much as laboratory experiments by comparing the results from numerical simulations and empirical equation. And for arbitrary Parshall flume, that is unlisted in the ISO standards due to environmental conditions, constructional difficulties etc, thus, the hydraulic experiments should be conducted to obtain the empirical formulas for it, the results from numerical simulations were compared with those of laboratory experiments. Consequently, it was convinced that the numerical simulation about Parshall flume was simulated appropriately instead of experimental approach. And the dimensionless discharge equation of arbitrary ones was suggested using the results of numerical simulations, and the equation was validated by comparing with laboratory experimental results showing the maximum relative error of 2.3%. If the actual topography, the shape of inlet and submerged flow, which is excluded in this study, were carefully considered, it would be possible to supply a simple empirical discharge equation based on numerical results. Also, it can replete hard works for hydraulic experiment being error-prone with complex procedures to a minimum of economic effort.