Export fluctuations are partly the result of coordination failure, some government intervention may be necessary. By borrowing the modern portfolio theory for selecting optimal export markets mix and better measuring export risks, this paper argues that it is theoretically feasible to propose a new index named relative variance as an alternative to variance and construct a model of export markets mix. According to this model and the data on China’s export, we calculate the efficient mixes of China’s export markets, which indicate that China should increase exports share from the rest of Asia (outside the 15 Asian economies), Africa and Latin America. And this adjustment is feasible both in theory and practice.