At present, overseas industrial parks have become an important platform for economic and trade cooperation between China and other countries involved in the Belt and Road Initiative (BRI), and they are playing an increasingly important role in the construction of the BRI. Most existing studies on overseas industrial parks of China focus on the economic function, while the institutional and cultural platform function need to be further explored. Based on the perspective of the institution and culture, the paper takes Sihanoukville Special Economic Zone in Cambodia as a case to analyze the operating mechanism and construction model of overseas industrial parks, and reveals the role of overseas industrial parks in promoting the outward foreign direct investment of Chinese small and medium-sized enterprises (SMEs). The results show that the Sihanoukville Special Economic Zone has provided a high-quality institutional environment and sufficient transnational development space for the enterprises entering the zone by constructing a multi-level coordination mechanism, creating an excellent investment environment, promoting information and resource sharing, and releasing the agglomeration economic effects. It assists enterprises in the zone to better adapt to the host country's investment, and provides more possibilities for a large number of small and medium-sized enterprises to make path breakthrough and path innovation in their overseas investments. On the basis of the case study, we believe that overseas industrial parks have played an important role in promoting Chinese small and medium-sized enterprises' overseas investment, providing buffer space and growth environment for overcoming institutional and cultural differences in Chinese enterprises' overseas investment, and played a role as an "Investor Garden".