The theories and discourses of urban planning have faced various developments in the last few decades Because the essence of the theory is transformational and affected by different vectors and forces in time and place, it undergoes many ups and downs. One of the topics that has taken on a more prominent role in urban planning systems in recent decades is issues related to citizen participation. Despite the importance of a participatory system for citizens, the theories proposed in this field lack the necessary capability and efficiency. The discourse of citizen participation refers to both the acceleration and threat of citizen participation. The main goal of this research is to discover the obstacles of citizen participation in the process of plan, process and preview (3p) from the point of view of urban planning professionals. The present study is fundamental in terms of its objective and falls within the category of qualitative and interpretive research. In this study, the grounded theory method (classical approach) and content analysis were utilized. The method of collecting information is through open questionnaires (completed with 176 professionals in the field of urban planning). Maxqda software was used for qualitative data analysis and coding. A total of 474 open codes have been extracted, and these open codes have been converted into 57 concepts, 21 sub-categories and finally 8 main categories. Lack of provision of platform and facilities, dominance of power, lack of transparency and trust, structural weakness and non-participation of the process, use of inappropriate methods, weak knowledge support and insufficient experiences, lack of popular acceptance, conflict of interests of different strata as key components in non-participation Citizens are known from the point of view of urban planning professionals. Comparison and comparison of the components mentioned in previous studies that investigated the non-participation of citizens in general and the components specifically mentioned by professionals in the field of urban planning regarding the non-participation of citizens In the triple processes of plan, process and preview, it shows that many of the mentioned components and factors are common.