At present， there are still considerable controversies about which term structure of risk-adjusted discount rate should be used in practice， and such controversies lead to different suggestions for similar investment projects． In order to solve this dispute， this article finds out the main factors affecting the structure of the discount rate from the perspective of the composition of capital productivity． By introducing the relative intensity of uncertainty from the future economy as well as from the project itself， the paper shows the relative intensity of uncertainty determines the coefficient of risk premium． It also shows that the coefficient of risk premium determines the term structure of risk-adjusted discount rate． The structure of the risk-adjusted discount rate is decreasing unless the coefficient of risk premium is greater than a threshold value．