Abstract: The paper chooses the four factors which affecting agricultural security under open economy, i.e. agricultural international competitive power index, foreign dependence degree of agricultural export, foreign dependence degree of agricultural capital, control rate of agricultural foreign capital equity constructing the assessment index system. By employing 1995-2009 data of the four indexes and factor analysis method, China's agricultural security is been estimated, and a conclusion is drawn that with the further expansion of China's market open degree, the continuous growth of utilizing capital and foreign trade, and further increasing of agricultural facing competition pressure, China's agricultural security problem has already and will become especially evident. Therefore, some countermeasures were proposed, such as feasibly increasing the strength of supporting agriculture and investing in science and technology, implementing agricultural industrialization business, developing preponderant agricultures, strengthening legislation, raising the level of attracting foreign capital, and enhancing the international competitive power of agricultural products.