Abstract: Aim To study the relationship between expansible and complexity of information systems structure. Methods The structural complexity influence on the nets nodes characteristic was analysed based on the Petri nets model of information systems and by the math tools in nets theory. Results The analysis results enunciate that if we want to capture a information system which has the power of expansion and the stable structure, it is necessary to cut down the complexity of structure and particularly, to cut down the complexity of relationship. Conclusion This analysis result may be used to analyse the performances of information systems.