Question

any one tell me what is the direction of electric dipole moment and give reason?

Answer 1

The direction of the dipole moment is in the direction of the position vector of the positive charge relative to the negative charge.
This is a convention thats followed.
Its useful because using the dipole moment vector, you can treat the (-ve, +ve) charge pair as a system and operate upon it.

the vector equation is -
p(vector) = q d(vector) , where d is the position vector of positive charge relative to negative charge