In this paper, according to the margin adaptive (MA) algorithm with fixed transmission rate, we propose a suboptimal MA Greedy algorithm with demand function. In this algorithm, the allocation process is divided into two separate steps, resource calculation and subcarrier allocation. With the employment of overload inhibition process, diversity scheduling method and demand function, we improve the traditional MA algorithms to reduce the computing complexity with subscribers’ fairness and Quality of Service (QoS) guaranteed. Utilizing the simulation with real-time services, we have proved that compared to static allocation algorithms, our MA Greedy algorithm could enhance the system performance by 5-6dB with low computing complexity, which is very close to the optimal MA algorithm.