In this thesis, the transition form factors of decay have been calculated in the frame work of light-cone sum rules,(LCSR) approach. The LCSR is appropriate for calculating the heavy-to-light transition form factors in low energy scale. The LCSR is a new form of the quantum chromodynamics (QCD) sum rules, developed by Shifman, Vainshtein and Zakharov (SVZ). This approach presents a marriage of SVZ sum rule with the theory of hard exclusive processes. In this method, SVZ vacuum condensates are substituted by light-cone hadron distribution functions of increasing twist. The transition form factors are very important in the high energy physics, since other physical quantities related to the decay, such as decay width, branching ratio and CP violation can be investigated by using decay form factors.