Nest site selection, as an important part of bird breeding, is a hot issue in animal ecology. In order to explore the nest site selection preference and the main influencing factors of Common Cormorant, a medium-sized wetland bird, we analyzed the nest characteristics, nest site characteristics and nest site selection of Common Cormorant in Longfeng Reserve of Heilongjiang Province from April to October in 2019 by Mann-Whitney U test and principal component analysis. The results showed that: (1) Common Cormorants preferred to nest in the areas where the trees were relatively short (P<0.05), surrounding shrubs were relatively short (P<0.01), vegetation coverage was low (P<0.01), the distance from human disturbance was far (P<0.01), and the distance from water surface was far (P<0.05). (2) The influencing factors of nest site selection were concealment factor (20.634%), nest stability factor and disturbance factor (27.614%), vegetation factor (13.901%), water factor (5.782%) and nest loyalty factor (5.069%). Further analysis showed that: (1) The Common Cormorants tended to choose nest materials of moderate thickness, which came from dominant vegetation, and nest depth increased with increasing latitude. (2) The characteristics of Common Cormorants nest vegetation were consistent with the trade-offs of energy domination, and the feces in nest enhanced the characteristics. Based on above results, it is suggested that the tall trees should be planted in the nest area of Longfeng Reserve.