中文摘要：

在明确粮食生产作为耕地基础性功能的前提下，从粮食安全的角度提出了2020年北京不同耕地保护目标下的3种情景模式，分析了各情景经过生产波动校正后单产情况，采用最小人均耕地面积法，结合粮食自给水平和规划人口数量测算了北京耕保需求的底线数量。结果显示，无论以何种目标进行耕地保护，北京的耕地保护压力都是严峻的。结合测算分析结论，并针对现有耕保政策对耕地保护单一采用数量约束指标的问题，提出“等效面积”的概念，采取综合权重系数方法对影响耕地质量和作物产量的基本因素和拓展因素进行了分析，将耕地实际面积转化为等效耕地面积。最后，从制度和政策方面分析了基于“等效面积”的耕保机制。

英文摘要：

Foodstuffs production is the basic function of the cultivated land, it refers to the food security in China. Both the quantity and quality of cultivated land for foodstuffs in Beijing turned lower in later years. In order to calculate the minimum area of cultivated land conservation in Beijing until 2020, three scenarios were set up for different targets ： （ 1 ） High quality cultivated lands are not protected strictly, the average quality of cultivated lands becomes lower, the value of unit yield was predicted from power model ; （2） Quality of cultivated lands maintain the status quo, the value of unit yield was set equal to the actual value of 2003 ; （3） Most of high quality cultivated lands are protected strictly, and the unit yield is improved by technical ways. Additionally, production fluctuation was calculated from historical yield records in recent years, and then adjusted unit yields in each scenario were ascertained. According to the food self-sufficiency and population prediction from the urban planning, the minimum area per capita and the minimum area of cultivated land in Beijing were calculated. The results show the enormous stress in cultivated land conservation. Under the scenarios 1 to 3, the amounts of minimum area of cultivated land in Beijing are 215 368.2 hm2 , 207 054.5 hm^2 , and 142 013.6 hm^2 respectively. However, the existing institution of cultivated land conservation focuses only on the quantity, while ignores the other factors related to the quality. The equivalent area of cultivated lands was thus put forward. According to the weight factors system, the actual area can turn to the virtual one with quality factors. Weight factors can be divided into basic and additional ones. Based on the concept of the equivalent area, a set of newly developed institutions and policies on cultivated land conservation can play a more active role in protecting high quality cultivated land and many other aspects.