A Photo of With My Classmates

We had graduated from high school.  I can't forget the time when we studied together.   and The happy or the sad memories we shared together. Time is like the water,you can't touch it ,but you can feel it.Those times are like the people in the photo, you can't touch them but you can feel them.

I have changed your last sentence to make the metaphor tie in with your title.  Also water can be touched and felt, otherwise you won't be cleansed when you are taking a bath or a shower.

A photo of my classmates

We have just graduated from high school. I can't forget the time we studied together and the happy or the sad memories we shared together.Time is like the water; you can't hold it, but you can feel it.

Good!

We have just graduated - relates to your situation now. If you use simple past (we graduated), you'd need to indicate when this happened.

We had graduated - is definitely correct, but needs an explanation. You use past perfect when you relate one past event to another. Although there isn't a second past event in the paragraph, it is implied because you talk about the photo (when this photo was taken, we had already graduated from high school).

I think hold is the better verb here for the water analogy. Of course, that implies water held in the hand. In English we would use sand as the analogy (which refers to hourglasses).