Abstract: This paper proposes an adaptive modulation algorithm to realize unequal error protection (UEP) transmission in data spread Orthogonal Frequency Division Multiplexing (OFDM) systems. Based on the fact that the original data symbols have the same transmission characteristic, we respectively research an UEP algorithm to maximize the transmission rate with given power restriction aiming at increasing channel capacity, and an UEP algorithm to minimize the transmission power with given rate restriction aiming at satisfying the users’ requirements. Both algorithms can guarantee the different transmission qualities and different transmission rates of different priority data, according to the data’s requirements. The simulation results indicate that the maximizing rate UEP algorithm can ensure the transmission quality requirements with maximal rate, as well as the minimizing power UEP algorithm can ensure the transmission quality requirements with minimum power. The results of comparison with corresponding traditional OFDM algorithms show that data spread UEP algorithm can reduce algorithm complexity greatly, can decrease the modulation parameters transfer evidently, and can balance between performance and complexity, thus it has better application value.