The invention relates to a principal component analysis based steel grade inquiring and contrasting system and belongs to the technical field of on-line data bases. The system comprises a data base server, a Web serve, a client and an application module, wherein the Web server is connected with a relational data base server, and the client is connected with the Web server; and the application module comprises a relational data base, a data entry module, a steel grade inquiring module and a steel grade contrasting module, wherein the relational data base is deployed in the relational data base server, and the data entry module, the steel grade inquiring module and the steel grade contrasting module are deployed on the Web server. Users send a Web request to the server through a Web browser on the client, and the Web server searches pages and transmits files to the Web browser on the client. The principal component analysis based steel grade inquiring and contrasting system has the advantages that steel groups are used as a data organization form, a multi-national steel and iron material layered model is established, width and depth of the model are not limited, index weight values of key chemical components are calculated in a data driven mode on the basis of the steel groups as units by means of a principal component analysis algorithm, and the similarity of overlapping degree weighting of chemical component intervals is calculated, so that accurate and reliable material inquiring and contrasting services are provided for the users.