I want to learn about Niemeier lattice and Leech lattice in it. I will be pleased if some one could introduce some books or Lecture notes to me.

The standard reference is Conway and Sloane. If this is too much, you could try Wolfgang Ebeling's book "Lattices and codes A course partially based on lectures by F. Hirzebruch." Advanced Lectures in Mathematics. Friedr. Vieweg & Sohn, Braunschweig, ISBN: 3528064978. This covers Venkov's classification of Niemeier lattices, and some properties of the Leech lattice 

