Under the complex situation of information asymmetry, the selection of IT outsourcing businessmen of small and medium-sized enterprises is a very complex process and is difficult to quantify fuzzy and uncertain factors. Three kinds of hetero-value judgement information such as numerical value, interval number and lexeme are used to analyze evaluation principle, which can provide reasonable guidance for information system outsourcing decision of small and medium-sized enterprises, among which, using dual lexeme and its mass operation operator to conduct language evaluation information treatment can effectively avoid information loss and distortion resulting from pasted language information treatment method to keep the integrity of the information.