The status and importance of the urban development plans and their evaluation through various methods is still an outstanding challenging issue in the academic and practical settings. Plan quality evaluation is known as an emerging methodology for assessing the quality of plans. It typically evaluate plans in relation to whether they contain certain desirable features, and aims to answer questions about the suitability of plans, applying methods and theories of planning, their strengths and weaknesses related to the ideal situation in different fields. During the past two decades, researchers have been able to formulate conceptual consensus based on the preliminary principles of plan quality. The purpose of this study is to introduce concepts and methods for plan quality evaluation describing an appropriate systematic conceptual model in order for quality evaluation of urban development plans in Iran, so that planners, while knowing the appropriate content of the plans, can try to carry out further research focused on specific topics and fields. It should be mentioned that the method used in this study is an explanatory overview. As the theoretical foundations, different methods and studies related to the subject have been comprehensively investigated and analyzed, consequently, the suitable "model and method" for evaluating the quality of urban development plans in Iran is clearly explained and adjusted to the whole country. In this research, six main stages for content analysis of the plans were clearly described including (1) determining the subject of evaluation, the level and scope of the research, explaining the conceptual model, identifying and determining the main features of the plan; (2) making a protocol composed of components, criteria and items (questions and items) related to each feature; (3) determining the method for scoring items in the protocol; (4) coding principles and methods; (5) checking the reliability of scores; and (6) interpreting, analyzing and comparing of plan quality scores. Additionally, due to the clarification of the concepts and theoretical framework and the literature review of the plan's quality, in order to explain the conceptual model of the comprehensive plans quality in Iran, the provisions of the definitions, requirements and methods of (rational) comprehensive planning, the description of contract services for the development plans (type 12), laws, guidelines, approvals and opinions of researchers, experts and critics of urban development plans, the results and content of studies on evaluation of plans in Iran were widely utilized. Finally, a conceptual model was designed with 10 main components (i. e., fact base, analysis and inference, preparation of plans, implementation, inter-organizational coordination, participation, presentation, monitoring and evaluation, planning methods, sustainable development). This conceptual model can be both a guide and a checklist for planners to improve the content of their plans and identify the strengths, weaknesses and shortcomings of them. Last but not least, this study motivates researchers to appropriately apply this conceptual model or counterpart models to their research topic for the purpose of initiating and extending studies on the quality of plans in Iran.