Abstract: This paper proposes a new adaptive bit and power allocation algorithm for single-user adaptive OFDM system so as to satisfy its user's QoS(mainly prefer to user's data transmission rate and(error) rate) requirement.This new algorithm tries to minimize the required transmit power per-bit when the bit is allocated.Simulations illustrate that in the same transmission circumstance,the total transmit power of the proposed algorithm is less than any other algorithm for this kind of single-user adaptive OFDM system,and its performance is better than any others.