Can a pronoun be simple subject?

Yes, a pronoun can absolutely be the simple subject of a sentence.

Here are some examples:

* She went to the store. (She is the subject)

* They are playing in the park. (They are the subject)

* It is raining outside. (It is the subject)

* We will go to the movies later. (We are the subject)

Key Point: The simple subject is the noun or pronoun that performs the action of the verb in a sentence.