A binary decision diagram (BDD) that expresses a logical Boolean function can be used for formal verification, and the order of BDD variables directly affects the size of BDD. In this paper, we present a new bidirectional fast BDD dynamic reordering algorithm based on variable swaps. The results of some benchmarks show that, it can reduce the runtime by 18%, the number of variables swaps by 21%, and even the size by 9%, compared with the classical sifting algorithm.