A spectrum allocation algorithm based on user allocation and load is proposed which includes two parts: User allocation sub-algorithm and spectrum allocation sub-algorithm. Based on the theory of cluster partitioning, an user allocation sub-algorithm is designed. This makes the users associate the same access point with similar signal noise ratios; therefore, this alleviates the popular near-far problem of wireless access network. Then, based on the user allocation results, a spectrum allocation sub-algorithm is designed for optimizing the spectrum allocation according to the load of each access point and the mean value of signal noise ratios of its associated users. The proposed algorithm is realizable, and has polynomial computation complexity and proportional fairness. The trace-driven simulations show that the system throughput is improved efficiently and the length of packet buffer is decreased profoundly by the proposed algorithm.