Title: Exploring Over-smoothing in Graph Attention Networks from the Markov Chain Perspective. Abstract: The over-smoothing problem causing the depth limitation is an obstacle of developing deep graph neural network (GNN). Compared with Graph Convolutional Networks (GCN), over-smoothing in Graph Attention Network (GAT) has not drawed enough attention. In this work, we analyze the over-smoothing problem in GAT from the Markov chain perspective. First we establish a connection between GAT and a time-inhomogeneous random walk on the graph. Then we show that the GAT is not always over-smoothing using conclusions in the time-inhomogeneous Markov chain. Finally,  we derive a sufficient condition for GAT to avoid over-smoothing based on our findings about the existence of the limiting distribution of the time-inhomogeneous Markov chain. We design experiments to verify our theoretical findings. Results show that our proposed sufficient condition can effectively improve over-smoothing problem in GAT and enhance the performance of the model.