is it true the chinese, korean, and japanese are all mixed of mongol blood?

You weren't paying attention in history class, were you? Human life started in Africa. People migrated from there. Then tribes roamed all over the earth for thousands of years. We are ALL mixed.

Even if there is a difference in the ratio of DNA, it is always included.

Practically every nationality is mixed. Europeans have been mixing for thousands of years and people all over the world have some degree of European ancestry. The same is true for Africa, Asia, the Americas and the Pacific. There are blacks on every continent. There are Asians in Africa and in the Americas. Unless you're from North Sentinel Island, chances are that you're not of homogeneous ancestry no matter what you yourself might classify yourself as being. 

It's not that simple.  

With DNA lineage tracking, they are finding that our ancestries are far more complicated than ever imagined.  For example, we are taught that Native Americans (aka, Indians) came from Asia.  They are Mongoloids like the Han Chinese, Koreans, and Japanese.But DNA tracking has revealed that at least several groups of indigenous Native Americans came from Siberia.  Yep, Russia.  If you're really interested in the subject of where and how the eastern cultures came from, I suggest you research it on the web...it's way too complex to handle in Answers.

Yes, most of them have that DNA (even though they don't like to admit it for some reason).