1. A sorting method of data documents, adapted to an electronic device, comprising: retrieving at least one first keyword from a content of a first data document; retrieving a keyword ranking corresponding to the at least one first keyword by a search engine; searching a keyword category corresponding to the at least one first keyword; and inputting the at least one first keyword, the keyword ranking and the keyword category of each of the at least one first keyword into a sort algorithm thereby outputting a predicting ranking of the first data document to sort the first data document, wherein the sort algorithm is generated based on contents of a plurality of second data documents and a current ranking of each of the plurality of second data documents.