Why equilbrium constant doesnt depend on concentration as it formula is concentration of product/conc. of reactant..??

Thats because if u change concentration of reactants at equilibrium, the conc. of products also changes such that the ratio of two remains constant. Hence eq. constant remains constant.

the corret formula of equlibrium constant is 

K=[C][D]/[A][B]

the concentrations here are the concentrations of the reacants and product at eqilibrium condition. at eqilibrium the concentrations are constant. as the reaction proceeds to equilibrium it reaches the concentration which are constant.that is why equlibrium constant is constant.

Hey ,equilibrium constant does not depends only the on initial concentration of the reactants