In this thesis, we extend the application of BCFW recursion relation to string tree-level amplitudes. In contrast to the field theory calculation, we encounter the difficulty of summing over all intermediate physical states with infinite tower of mass levels. We develop a method to resolve this difficulty by enlarging the sum over all intermediate physical states to an easier sum over the entire Fock space of string spectrum. The calculation is successfully applied to the 4-tachyon amplitude and then to the cases of one arbitrary higher spin state and 3-tachyon amplitudes. We also figure out a generating function for summing the infinite poles of string spectrum in the BCFW string amplitude calculation. The generic structure of this generating function for higher spin scattering amplitude can be obtained from the standard path integral calculation of string scattering amplitude.