Abstract: The lack of appropriate review methods has led to disputes over the hierarchy of the principle of legitimacy of purpose,as well as issues such as review misalignment,insufficient review,excessive subjectivity,and inaccuracy caused by some scholars simply copying the principle of reasonableness of common law to determine the inappropriate purpose in the principle of proportionality.The key to solving the problem lies in reconstructing the method of examining the legitimacy of the purpose.The principle of proportionality,the common methods of law and economics,and negotiation theory can be integrated to construct a new approach for examining the legitimacy of purposes.Starting from the “comparative” thinking,the purpose of examining the legitimacy of purposes can be classified into two categories: “the purpose of realizing (safeguarding) rights (interests)” and “the purpose of restricting rights (interests)”,and the corresponding objective and subjective content can be compared and examined.In the review process,the objective content corresponding to the purpose should be quantified and reviewed first,and then the subjective content corresponding to the purpose should be reviewed.In terms of examination standards,based on the improvement of Kaldor Hicks,the objective content corresponding to the legitimacy examination standard quantified by law and economics is that the value of “realization (protection)” is greater than “limitation”; The examination of subjective content corresponding to the purpose is achieved through equal and free negotiation.The objective and subjective content corresponding to the purpose has passed the legitimacy review,and the purpose is legitimate.By combining the advantages of the principle of proportionality and the principles of law and economics,and using the common “comparison” method of proportionality,law and economics,and negotiation theory as the connection point,we can better understand and practice the principle of proportionality.