Semileptonic decays play an essential role in the determination of the CKM matrix elements. We review the current status of theoretical calculation of semi-leptonic $B$ decays, focusing on the method of light cone QCD sum rules. In this approach, people calculate the suitable correlation function with weak current between vacuum and B meson or light meson light cone distribution amplitudes. By using the dispersion relation and quark-hadron duality, we can get the corresponding transition form factors in the large recoil region. Recent progresses have been made up to the two loop QCD corrections and next-to-leading power corrections. These improvements combining with the lattice QCD results at small recoil region, have significantly improved the theoretical precision of $|V_{ub}|$ and $|V_{cb}|$ determination. We emphasize the importance of the non-perturbative input of meson light cone distribution amplitudes in these studies.