American agriculture is a typical modern agriculture. In 2000, the total agricultural output value was $810.2 billion, accounting for10.5% of the gross national product. The output of major agricultural products such as wheat, corn, soybean and cotton ranks among the top in the world, and the grain output accounts for 20% of the world's total output. The foreign exchange income from the export of agricultural products reaches 40 billion dollars every year, which is the largest foreign exchange income in the United States. The basic production unit of American agriculture is family farm, and there are 2173,000 farms in China. Agricultural land is 430 million hm2. After the 1940s, American agriculture realized mechanization, modernization, specialization and high technology. Modern large-scale agriculture has created extremely high labor productivity, which makes the output of various agricultural products in the United States greatly exceed the maximum demand in the domestic market. Therefore, American agriculture must export a large number of agricultural products to overseas markets.