We investigate the coherent tunneling phenomenon of the laser-driven atomic ensembles confined in a well-separated double-well potential. By generalizing the Frohlich canonical transformation to adiabatically eliminate the light field variable, a BCS-like effective Hamiltonian is obtained to depict the residual interaction between the two atomic ensembles. The number of the tunneling collective low excitations and its relationship to the ratios gr/gl and Nr/Nl are given.