As the largest developing country in the world, China has been actively undertaking the responsibilities and obligations of the international community, and has helped other developing countries, especially the least developed countries, to expand their trade by unilaterally providing zero tariff treatment and assistance within its capacity. In order to test the effectiveness of the two policies, this paper studies the impact mechanism of the two policies on the export diversification of recipient countries under the same framework, and uses the data of China and Africa for quantitative evaluation. The results show that China’s zero tariff treatment on African countries has a significant positive effect on the export diversification of recipient countries, while the promotion effect of aid on the export diversification of recipient countries is not obvious. These conclusions are still robust when minerals are excluded and different export diversification measures are used to test the original model. Therefore, in order to more effectively support African countries to improve export diversification, China needs to construct a dual development strategy including zero tariff treatment and Aid for trade.