Over two decades, distribution of China’s soybean import sources changed significantly. Price as is implied in traditional HO theory is unable to justify that change. Instead, the seasonality of agricultural production may contributes more to changes on import source of soybean by seasonal supply constraints. Based on exporters’ decision-making behavior, this paper analyzed the impact of constraints from exporters’ exporting prowess on China's import source distribution from the perspective of seasonality, using monthly data of China and the three major soybean exporters from the year 2010 to 2013. Empirical results show that an exporting country takes up a significantly bigger share in China’s soybean imports in its harvest season than in non-harvest season. Changes on import source result from dynamics of comparative advantage of exporting countries. Taking seasonal complementarities and comparative advantages of exporters into consideration, China may make good use of world resources and stabilize domestic supply of food.