How to improve the efficiency of exact learning of the Bayesian network structure is a challenging issue. In this paper, four different causal constraints algorithms are added into score calculations to prune possible parent sets, improving state-of-the-art learning algorithms' efficiency. Experimental results indi-cate that exact learning algorithms can significantly improve the efficiency with only a slight loss of accuracy. Under causal con-straints, these exact learning algorithms can prune about 70%possible parent sets and reduce about 60% running time while only losing no more than 2% accuracy on average. Additionally, with sufficient samples, exact learning algorithms with causal constraints can also obtain the optimal network. In general, adding max-min parents and children constraints has better res-ults in terms of efficiency and accuracy among these four causal constraints algorithms.