Marriage confusion

it's legal or not ?

Hindu Marriage Act -

 5(iv) the parties are not within the degrees of prohibited relationship unless the custom or usage governing each of them permits of a marriage between the two;

5 (v) the parties are not sapindas of each other, unless the custom or usage governing each of them permits of a marriage between the two;

If Grandfather is From Father side, she will be come Sister - "NO"

If Grandfather is from Mother side, then you can marry, as She become "Cousin",  This is valid in Certain states only, Otherwise NO

Thanks for ans. ok. it's from my father side, From u r point it's not legal. then i just want to know it's like a long distance relationship or closer ?

This is close relationship, as she is with in 3 levels. This rule is based on Custom / usage in that Area  / Caste/ sub caste. If that is against, then this is Definitely Not advised.

unless you have totally different intention, you may need to check with Advocate in your area,

thanks a lot. 

You will be marrying your sister.  It is against law.  It is a sapinda relationship.  Barge in and you wil have kids born with physical and mental deformities.