Based on the entrepreneurial ecosystem concept proposed by the environmental determinism school like Cohen and Isenberg, factors influencing unicorn growth are summarized into six aspects: local policy, economic market, human capital, financial investment, entrepreneurial culture, science and technology. Taking Ant Financial as an example, the most valued unicorn in China, this paper analyzes the influential mechanism of local entrepreneurship ecosystem on unicorn growth from the above six aspects. It is found that: ①the rapid growth of a unicorn firm needs the support of local entrepreneurial ecosystem, while the local definitive industrial development direction, good human resource environment and unique entrepreneurial culture are particularly important; ②the talent enabling, technology empowerment and capital investment of local platform firm play an important role in promoting the rapid growth of unicorn firm, and also make them start a business from a higher starting point; ③different supporting systems are needed in different stages of unicorn firm’s development. In the incubation period, the support of local industrial policies and platform firm’s human capital is prominent. In the growth period, the support of local market demand and platform firm technology is very important. In the mature period, local entrepreneurial culture and platform firm’s capital investment is very important.