Here’s how I would write it.

I always think that time will stand still during the summer.  As I walked home today, there was a cool breeze blowing and a leaf floated down from a tree and landed near my foot.  I was surprised, looked up and saw that the sky was so blue and clear.  At that moment I realized the summer was almost gone and we were already in mid-autumn.  Today is September twenty-ninth.  Last year at this time I had just arrived in Xinjiang from Shandong.  The year has passed in a flash.  I’m already a different person from what I used to be.  I don’t know how long I’ll be here but I know I’ll have to leave some day.

 Your words remind me of a song I learned in my youth.

Ach wie bald vergehn die schönen Stunden,
die wie Wolken verwehn
So ein Tag, so wunderschön wie heute,
So ein Tag, der dürfte nie vergehn.

Oh now soon the happy hours go by,
just as the clouds blow away.
Such a day, as beautiful as today,
Such a day, should never go away.

Summer have is gone

I always think that time is still stay in the summer, I always think that it is still summertime, but walked on the way home, there was a cool breeze. The wind blew over, then a (slice of) leaf floated from the tree (You could say: Then a leaf fell from a tree) and stopped near my foot. I was really shocked and looked up. The sky was so blue and pure. At that time, I found out / realized that the summer had almost gone ended, and the time have it is now full into the mid-Autumn already.
Today is September 29th. At the same time in the last year, I arrived in Xinjiang from Shandong. A year has past in a flash, I am already not what I am at the first, and I have already changed since I arrived. I don't know how long I'll stay here, but I know, I'll have left here one day. leave here one day.

I'm not sure what you were trying to say at the end T-T