The article encodes the data of piracy cases in recent ten years provided by the international maritime administration and splits the cases into nine variables: the occurrence sea area, whether the pirates boarded the vessel, the status of infringed ship, the type of vessel infringed, the registry of the infringed ship, carrying weapons by the pirates, the number of pirates, the treatment method, and the degree of infringement of legal interests, of which the first eight are independent variables and the degree of infringement of legal interests is dependent variables. It is concluded that the occurrence sea area, ship status, ship type, weapon carrying situation, and handling measures after piracy will generate significant impact on the dependent variables. In the dependent variables, there are five categories divided into potential damage offense, attempted infringement of property, accomplished infringement of property, complete violation of human health, complete violation of property, and human health, with the degree of legal interest violation increasing gradually. The Chi-square test shows that any of the independent variables will have an impact on the dependent variables. The evaluation of piracy by means of combined punishment for several crimes will fully take into account the development of piracy and the situation of the accomplished and attempted acts, so as to achieve the compatibility of crime and punishment.