We consider the axial-vector mesons K_1(1270) and K_1(1400) as a mixture of two |^3P_1rangle and |^1P_1rangle states with the mixing angle theta that equal to (-34pm 13)^circ . We calculate the light-front distribution amplitudes (LFDAs) and decay constant formulas for both the axial-vector mesons K_1 in the AdS/QCD correspondence. The transition form factors of the semileptonic Brightarrow K_1 decays are derived in terms of the LFDAs for K_1 mesons. Using these form factors and decay constant values, the differential branching ratios of Brightarrow K_1 (1270, 1400) ell ^+ ell ^-, ell =mu ,tau transitions are plotted with respect to the four-momentum transfer squared, q^2. In addition, the branching ratio values of these decays and the non-leptonic B rightarrow K_1(1270, 1400) gamma decays are estimated. A comparison is made between our results for the branching ratios of Brightarrow K_1(1270, 1400) gamma decays in the AdS/QCD model and predictions obtained from the light-cone sum rules (LCSR) as well as the experimental values. Finally, the forward-backward asymmetries for the aforementioned semileptonic decays are plotted on q^2 in both the AdS/QCD correspondence and two Higgs doublet model (2HDM) in order to test the standard model (SM) and search for the new physics (NP).