My daughter is afraid of her father, and there is nothing to talk about with him (because he always keeps a straight face). How can we make the relationship between father and daughter harmonious?

Dad's straight face is caused by his habit, not that he doesn't like you.

As the father of his daughter, he must love you very much, but he didn't express it.

Talk to dad more at ordinary times, and don't care about his expression.

For example, communicate with him more about things you are not sure about.

Listen to his opinion, and you will get along slowly.