Abstract: As economic developed so quickly, the industrialization’s fast expansion cause land for construction increased quickly. This article take Rudong County as an example, after invested the situation of land utilization in countryside at present time and the condition of cultivated land and the economical situation of Rudong county, consulted lots of materials.Based on analysis of the relation among economic development(GDP), investment increasing, population, urbanization and quantity changes of farmland in Rudong county, the author found that the investment and urbanization are the most important factor that leading the changes of farmland. At last pointed out the countermeasure of farming protection.