A dynamic access selection algorithm based on load balance is proposed for heterogeneous wireless networks. To adjust the network load to reach an ideal state, the algorithm not only considers user mobility, user satisfaction and available bandwidth of each network, but also considers the influences of selecting different access networks on the overall call blocking probabilities. Simulation results show that the proposed algorithm can dynamically adapt to the network load and lessen the unbalance of call blocking probabilities among candidate networks, and thus effectively reduces the average call blocking probability of the whole heterogeneous system.