中文摘要：

针对目前净现值计算公式中通常使用固定折现率的情形，提出将折现率分为动态无风险折现率和动态风险折现率。利用国债利率期限结构模型确定无风险折现率，给出了四种情形下的净现值计算公式，并通过两个数值算例给予具体说明。修正后的净现值公式能够对任意时刻的现金流进行准确折现，更加符合投资项目评价的实际。

英文摘要：

At present, the fixed discount rate is mostly used to compute net present value （NPV）. This paper proposes the new idea that the discount rate should be divided into a risk-free discount rate and a risk discount rate. The risk-free rate can be determined by using the term structure model of treasury interest rates, and gives formulae for NPV under four different situations. The cash flows over arbitrary time can be accurately discounted with the modified formulae for NPV, and correspond to the actual situations pertaining in investment project evaluation and financial management. Finally, two numerical examples are presented to illustrate the practicality of the formulae derived.