As an important part of urban human settlements, urban green spaces are widely recognized for their social, economic, and ecological benefits. In the context of rapid urbanization, urban green spaces, as an important component of the urban living environment, have gradually attracted widespread attention from government departments and scholars from various disciplines due to their significant role in public health. Therefore, it is of great significance to study the mechanism of its influence on residents' mental health for health-oriented planning and design. While their impact on residents' mental health has been extensively researched, there is a lack of focus on the role of obstacle factors that may mediate the effect of perceived quality on mental health. Specifically, existing research has primarily focused on exploring the mediating role of motivational factors such as physical activity, social cohesion, and stress recovery, while insufficient attention has been paid to the role of barriers. This has led to a neglect of the mediating effects of objective barriers related to green space characteristics and the moderating effects of subjective barriers associated with individual traits. Drawing on the "Motivation-Obstacle" relationship model, this study conducted a survey of 520 questionnaires in Wuhan in 2023 to explore the mediating effect of objective obstacle factors and subjective obstacle factors on the influence of public perception of urban green space on their mental health. The objective barriers of urban green spaces are defined as the characteristics of green spaces that do not meet visitors' needs for access to nature. Subjective barriers related to urban green space are defined as that there are some characteristics inherent to urban residents that hinder their ability to engage in healthy behaviors. The findings indicate that: (1) Public perception of the quality of urban green space is positively associated with their mental health. (2) Public perception of the quality of urban green space can indirectly impact their mental health by reducing objective obstacles to visiting urban green spaces, with this mediating effect being more pronounced in the group with children. (3) The subjective obstacles faced by residents have a significant moderating effect on the mediating role of objective obstacles in the relationship between the perceived quality of urban green space and mental health. The study suggests that in addition to enhancing the characteristics of green spaces to reduce objective obstacles, future planning and design of urban park green spaces should also focus on encouraging and guiding residents to adopt proactive health behaviors through urban green spaces.