Floodplain analysis is usually used in hydrology for calculating the possibility of high water stage features. Floods are treated like a human problem. In the concrete case was taken maximum annual stage data for a period of 34 hydrologic years (1971/72-2004/05) for Gauge station “Demir Kapija” on River Vardar and Boshava. The analysis is created using some probability distributions like Normal, Pearson distribution type III, Gumbel distribution, Log-Pearson distribution type III and Lognormal distribution. Calculated results from the water stage frequency analysis are treated with the Kolmogorov-Smirnov test and χ2 test for obtaining best fitting distribution with empirical Weibull formula. The frequency distributions results were plotted on probability paper and compared with empirical Weibull points besides the statistical testing. The best fitting distribution is Lognormal. Maximum theoretical stages of best fitting distribution for different return periods were mapped on the rivers Vardar and Boshava banks in Tikvesh Valley. The map presents all flooded areas in treating territory for different return periods.