Abstract: The idea of principle of proportionality is embedded in the principles and rules of personal information processing. How to apply the principle of proportionality and play its role of instrumental rationality in personal information processing is an urgent problem of grasping the norm and connotation of personal information processing. The principle of proportionality has the characteristics of economic efficiency. Therefore, it is necessary to analyze the economic logic applicable to the principle of proportionality in personal information processing. The review structure of principle of proportionality in personal information processing is constructed to enhance applicable rationality via instrumental rationality, and meanwhile, the cost-benefit theory is introduced to make better analysis. In view of the limitations of principle of proportionality in personal information processing, a boundary between personal information and personal data should be set and type-based application of principle of proportionality should be advocated so as to balance the protection and reasonable usage of personal information. 

Key words: personal information processing, principle of proportionality, cost-benefit theory, balance of interests