In this work, we develop an algorithm based on finite-temperature time-dependent density matrix renormalization group (FT-TD-DMRG) in the grand canonical ensemble to calculate the power factor of organic materials described by Holstein model. We demonstrate that FT-TD-DMRG is a powerful method for investigating the organic thermoelectric transport process, which can bridge the gap between hopping picture and band picture. Detailed theoretical framework and numerical outcomes are provided in the following sections.