I wrote corrections in ALL-CAPS for visibility. When I eliminate a word, I use XXXX to draw your attention to that fact. Note that your writing about a movie should be mostly in the present tense, known as the “literary present.” I’ve used an asterisk (little star *) to mark a certain error that you make systemically — see if you can figure it out. Here we go:

Coco, a Disney cartoon XXXX* directed by Pixar, IS* about a marvelous (OR “AMAZING” OR “WONDERFUL”) adventure THAT* happens to a boy who PURSUES the dream (BETTER “… A FANTASTIC ADVENTURE THAT A BOY HAS WHILE PURSUING HIS DREAM…..”)  to be a musician and his ???? great-great-grandfather.

It is a really touching movie for me. Not only do it have the superb special effect, it also has fabulous plot. The real death is that no one in the world remembers you, is really inspired me. I realize that death is not a awful thing, i don't afraid of it no longer. Although it will cause culture shock, you will indeed be touched by family connection.

At first, Miguel, a 12-year-old boy from Mexico (FROM OR IN MEXICO, OR IS HE “A 12-YEAR-OLD MEXICAN BOY”), regards music as his life while his family forbids anyone in THE family to do music, INSISTING THAT THEY make XXXX shoes, because his great-great-grandmother WAS abandoned by his musician husband. Thus, Miguel has to play the guitar in a CRAMPED dark attic SO that no people (better “NOBODY”) WILL find him. 

On the Day of the Dead, Miguel steals a guitar and the most amazing thing happens; he enters the Land of the Dead. Besides he finds his family members who have died. He still insists ON PURSUING his dream regardless of the disagreement of his family. Next, he meets XXXX Hector, a great musician, (WHO is)* a father who is eager to see his daughter. Miguel promises TO help Hector (to) put his photo on the shelf if Hector CAN help Miguel (to) make his dream true. After that, they meet a lot of stuff (CORRECT, BUT VERY UNNATURAL), for example, THEY HAVE SEEN Hector's friend’S DEATH, MET XXXX Miguel's family (ANCESTORS?) and FOUND OUT the real REASON why Hector dead and (“THAT”) Hector is Miguel's great-great-grandfather (THE LAST SENTENCE IS REALLY HARD TO UNDERSTAND, SINCE I HAVEN’T SEEN THE MOVIE). In the end, the family GETS together to send Miguel BACK TO THE WORLD OF THE LIVING, Miguel puts Hector's photo on the shelf and remindS his mama Coco of his father (WHAT DOES THE LAST SENTENCE MEAN?.

Good job! By the way,

较点儿短的文字将会吸引更多的改正。

Also, it’s a good idea to post when people in your target language time zone are awake — like I did. Welcome to italki!