We highlight the advantage of the present method for intermediate coupling regime, difficult for other approximate methods. Our method can bridge the gap between hopping transport described by Fermi's golden rule and band transport described by Boltzmann transport equation, providing a unified picture for organic materials' thermoelectric transport process. We find that (i) electric conductivity and Seebeck coefficient strongly depend on doping ratio and present impressive symmetry about 𝑐𝑐 = 0.5 in room temperature; (ii) increasing transfer integral changes the transport mechanism from hopping to band-like and enhances power factor monotonically. By merely changing the exact form of Hamiltonian and current operators, it is straightforward to take other factors into account in our framework, such as offdiagonal dynamic disorder, Coulombic interaction, static disorder, and so on.