中文摘要：

在我国的快速城市化进程中，农地面临着向市地流转的巨大压力。本文基于社会理性决策者为农地城市流转决策的决策主体和决策结果取决于流转前后社会收益与社会成拳的比较这两个基本假设开展研究，探讨了农地城市流转过程中存在的不确定性与不可逆性及其对农地城市流转决策的影响。结论认为，农地城市流转过程中客观存在着不确定性与不可逆性，其中各种不确定性最终反映在农地城市流转的社会收益、成本及净收益的波动上，而不可逆性与不确定性共同决定了社会决策者在制定农地城市流转决策时，必须充分考虑选择价值的重要性及其对决策的影响（降低决策者对未来收益的预期并促使其延迟决策）。忽视农地城市流转中的不确定性将导致决策结果产生或大或小的偏差，从而导致一定的经济、社会及生态损失，而忽视不可逆性将直接造成决策后果出现不可逆转性损失。

英文摘要：

Rural land is faced with tremendous pressure of being converted to urban land in the course of rapid urbanization in China. Discussions in this paper are made on the basis of two basic assumptions, which are： 1） decision-making subject is a rational social decision maker; 2） decision result depends on the comparison between social benefit and cost of rural-urban land conversion. It researches into the uncertainties and irreversibility in the course of rural-urban land conversion and how they influence decision making for this conversion. The results show that： 1） Uncertainty and irreversibility exist objectively in the course of rural-urban land conversion. Various uncertainties can be reflected from the fluctuation of social benefit and cost which occurred during rural-urban land conversion. All of these uncertainties would increase the difficulty of predicting the outcomes of the decision accurately. Irreversibility calls for a more cautious attitude of the decision makers to think over the option value which originates from postponing the decisions. Ignoring uncertainties in the process of rural-urban land conversion can bring about biases, which would definitely cause economic, social and ecological losses, and neglecting irreversibility will lead to irreversible losses directly; 2） On the one hand, social cost of the conversion will present an incremental trend at an uncertain growth rate in general. However, social benefit of the conversion can fluctuate either up or down. Both of them can result in the uncertainty of the fluctuation direction of social net profit finally. Therefore, it is profitable to postpone rural-urban land conversion decision in order to obtain more information which can help to make decisions more reasonable; 3） The existence of option value reduces the decision makers＇ anticipation about the profit that comes from rural-urban land conversion. The more they are averse from the risk and greater the uncertainty effects, the lower their anticipation will be and higher of