Beginning from St.-Petersburg foundation, floods negative impact at its population and harm to the city economics. During the analysis of historical dynamics of Neva floods all observation period was divided by climatic periods with duration of thirty years. Data show, that in last thirty years the quantity of floods was maximum during the whole history of observation and made up 63, that more than 40% higher in comparison with period 1949-1978 years. Maximum of flood quantity displaced from autumn on winter during last thirty years, their quantity sharply increased especially in January -several times. Statistical significant correlation factor between the flood quantity and the factor of Northern Atlantic Oscillation, characterized the intensity of cyclogenesis make up 0.54. Schema of the potential flooding of St.-Petersburg territory at increase of Gulf of Finland level on one meter was made up in accordance with data of climatic scenarios HadAM3H and ECHAM4/OPYC3. In case of this scenario, flood area will be 1362 hectares. Great natural and historical and cultural objects namely: beaches of Kurortnyi region, Yuntolovskyi national park, park «Dupki», land complex «Stenbok-Fermor» and others will be fallen within flood area.