This article uses an institutional approach to design a model for evaluating the Iranian public policy. The proposed model is based on the institutional characteristics of Iranian political system, and is therefore called an institutional modeling. An institutional model is considered a multi-approach and multi method model which takes a systematic approach. The main components of this model are: 1- Evaluation Goals: this component determines definition, types, stakeholders and functions of evaluation. 2- Policy Areas: This component identifies the right weighting of the five criteria and the limitations of evaluation. 3-Legislative Duties: This component identifies the level of policies and the purpose of the organization for the evaluation. 4- Organizational Characteristics: This component specifies applicable evaluation models according to the role, quality and quantity of expert personnel, quality of reporting and the internality or externality of it. The institutional model tends toward the division of labour, but applies it based on the evaluation being internal or external. In addition, by emphasizing on the complex relationship between stakeholder institutions and the necessity of managing that relationship, it considers the evaluation of policies as a coordinating and policy making tool.