If everybody DNA is different then how blood can match even with matching blood group?
A few components to my answer.


Red blood cells do not contain a nucleus, therefore, they do not harbour DNA.
The major determinant of blood compatibility is the blood antigen. There are only 4 types: O, A, B, AB. This is genetically encoded, and is expressed as a set of sugar coats on the blood cell membrane. However, the enzymes that encode for A or B should be identical from person to person.


I hope this gives you a preliminary answer to work off.