This paper develops a nonlinear spatial equilibrium model for analyzing the policy issues of international trade under imperfect competition. By introducing the mixed complementarity problem into the spatial equilibrium analysis, this model can be applied to evaluate issues about international trade and domestic support policies, including specific tariff, ad valorem tariff, tariff quota, export subsidy, production subsidy, production quota, consumption tax, and price floor. This model is then used to simulate international wheat trade with several supposed scenarios based on proposals for the new WTO agricultural negotiations from various countries and the agreement between China and the United States concerning China's accession to the WTO. The main findings of the simulations are as follows: 1. An extension of the existing WTO agricultural agreement would be favorable to the EU's wheat sector. 2. No great structural changes in wheat trade may arise if China joins the WTO. 3. Compared with the situation concerning an extension of the existing WTO agricultural agreement, the U.S. and the EU would markedly decrease their exports if the new WTO agricultural negotiation results were favorable from the point of view of exporting or importing countries. In either situation, China would increase its exports. 4. The inverse correlation between import volume and domestic production implies that almost all importing countries would be affected by the results of new WTO agricultural negotiations.