Rare and semileptonic decays of B-meson have provided much of the excitment in B-physics during the past several years, and the list of rare decays that are trraped by physicists in particle detectors one by one is continuously increasing. On the other hands, investigating rare decays of hadrons containing a heavy b quark, provide a powerful tool for physicists, which can ultimately leading to discoveries in physics of beyond of the Standard Model (SM). In this thesis, we have studied and calculated the transition form factors of rare semileptonic rocess, in the content of SM. The decay occure at loop levels by the electroweak penguin and box diagrams via the flavor changing neutral current transition of ,and there is no way to do it through a tree level in the SM. Transition form factors are the essential quantities, that we have described and analyzed in this dissertation. Using the mentioned form factors we can calculate many phenomenological observables related to the above decays, like: brabching ratio and etc.We calculate the form factors of the aforementioned exclusive decay in the frame work of the Light Cone Sum Rules (LCSR) with the B-meson distribution amplitudes. QCD light cone sum rules method is one of the most powerful and applicable non-perturbative model for determine parameters of hadronic states. The main object in this approach is the investigate correlation function, which we consider and calculate it in the quark and hadronic approaches, and then, by equating two diffrent representation of the correlation function via the dispertion relation, we will be able to extract the form factors of semileptonic transition.