The improvement of urban congestion and the mood of the populace is vital for achieving the United Nations Sustainable Development Goals. This paper aims to test the hypothesis that crowding in urban micro public spaces (UMPSs) affects emotions, and two different methods were used: a psychological questionnaire to measure whether crowding in such spaces elicits negative emotional responses from users and a portable electroencephalography (EEG) device to explore emotional responses. This study was conducted in Shenyang, China, based on the city’s relevant policies and the type and number of micro spaces and micro public spaces, proving that Shenyang City has paid more attention to planning micro spaces and micro public spaces in its urban development. The results show that 1. UMPS crowding awakens negative emotions in users, which affects their intention to revisit the UMPS, and 2. If the UMPS is more attractive to users, it also improves the negative emotions due to crowding, which implies that the attractiveness of the environment does play an important moderating role. This study may inspire the construction concept of UMPSs in different countries and cities, complementing the planning of urban public spaces to provide more social equity. The creation of UMPS has a positive effect on neighborhood interactions, community network construction, and the reproduction of social capital, which can contribute to the sustainable development of cities.