Abstract The aim of the present study was to design and apply the citizen participation optimization model in the public policy-making process with the aim of developing the green space of the Tehran Metropolitan Area. The present study is applied in terms of purpose, exploratory in terms of data collection method, and qualitative and quantitative (mixed) in terms of data nature.QDA2018 software environment. In the quantitative part, the data were analyzed using exploratory and confirmatory factor analysis methods with SPSS and AMOS software. The statistical population in the qualitative part included academic elites from management disciplines and green space managers of Tehran Municipality, who reached with 25 experts. To measure the model, a researcher-made questionnaire was distributed among 285 samples using the relative cluster sampling method. The reliability of the questionnaire was obtained as 0.78 using the Cronbach's alpha method. The results of the optimizing citizen participation in the public policy-making process with the aim of developing green space in the Tehran metropolis had 15 dimensions, as follows: causal conditions (Responsibility and commitment, Continuous interactions, Education and learning), background conditions (Development of a green tax package, Culture building, Managers' attitude and awareness), intervention conditions (Green strategy, Modern facilities and equipment, Technology and technical operations), strategy (Medium-term and long-term municipal policies, Continuous monitoring and evaluation, Citizen consumption management programs, Urban pollutant management programs), and outcome Development of urban green space, and Reduction of urban pollution). The results of the quantitative section showed that all dimensions of the research model were confirmed.