The public open space is the carrier of social, economic and cultural activities for the residents. In the process of urbanization, the public space is constantly compressed. Social interaction serves as a link between communities and plays an important role in the sustainable development of residents' life and the whole society. However, differences and gaps in space and culture make social interaction less frequent that community members are reluctant to communicate with each other. This had adverse effects on public life and the physical and mental health of individual residents. This research summarizes the importance of social interaction with literature review. It also highlighted the underlying determinants of providing attractive open spaces in mixed communities to encourage interaction. The study of the leisure behaviour of different groups of people also emphasizes the basic understanding of the ideal way of living for all groups and the use of public places. The case study puts forward the possibility of space arrangement of public space, encouraging public participation in design and construction, renovation of existing facilities and promotion of sustainability. This research attempts to combine these findings into a comprehensive study of public open spaces in complex communities. From the key findings, a practical toolkit is proposed. The toolkit includes physical design principles as well as policies to support the provision of spaces that are attractive and able to encourage interaction by promoting participation, shared activities, joint design and overcoming physical barriers. Then, on the application side, a site was chosen from a fast-growing city in a developing country to gain a broader perspective. The toolkit was configured at the site to test and evaluate its usefulness and feasibility. It's also used to spot potential conflicts. The research aims to promote public interaction and encourage people to live more sustainable lives.