1. Different definitions: the spot interest rate is the yield to maturity of zero coupon bond where the maturity date is set, representing the income from now (t is equal to 0) to time t, and the forward interest rate refers to the forward price of funds, which refers to the interest rate level from one point to another in the given spot interest rate.

2. Different functions: Spot interest rate is the basic interest rate and tool of financial market. Forward interest rate has always been a reference tool for the central bank to formulate and implement monetary policy. In mature markets, the pricing of almost all interest rate derivatives depends on forward interest rates.