"Tomorrow I die. Tomorrow I die, and today I want to tell the world what happened and thus perhaps free my soul from the horrible weight which lies upon it." by Edgar Allan Poe in "The Black Cat" short story. So my question is what tense is used for "Tomorrow I die" sentence?
That is the "simple present tense", which (although it is called a present tense) can also be used for future events, especially when the speaker believes that they are absolutely certain and unchangeable.
The use of the simple present with a future adverb like "Tomorrow" is a rhetorical and poetic effect, which means "Tomorrow I will die, and nothing can be done to change this fact."