Abstract: The determination of the interest rate is the core element of the notional defined contribution (NDC) system, and it is also the main basis for the choice of the interest rate index. The interest rate is essentially equivalent to internal rate of return of PAYG pension system. By combing the relevant theory, induction and deduction, the interest rate is essentially the economic growth rate at the Golden Rule level rule. However, due to subject to the actual operation of the economic, population and pension system, there are very obvious limitations for the application of the theory.