Relationship and Effect Between InvestmentPayoff Period and Discount Rate in the Economic Value Quyang Qiaolan\ Lin Genxiang [WT5”BZ〗\ The key paramters which dictate the acceptability of a project are its dynamic & static westment payoff period, its FNPV and ENPV, while the standard to judge its value is its datum discount rate and social discount rate.This article analyses the relationship between investment payoff period and discount rate, and studies the methods to determine investment payoff period and discount rate when we assess the economic value of a project.:[WT5”BZ〗\ investment payoff period;\ discount rate;\ financial net present value(FNPV);\ economic net present value. Ouyang Qiaolan:[WT5”BZ〗\ Engineer, Institute of Design, WUT,Wuhan 430070, China.