We explore distance dependent variation of the coherence length relevant to DNA charge-transfer processes within 5'-GAnG3-3' DNA sequences. Recently developed on-the-fly filtered propagator functional path integral approach was employed to sort out transport trajectories with significant contribution and to analyze correlation between electronic states. In particular, the coherence length was quantitatively determined through characteristics of off-diagonal quantum trajectories. Simulated coherence lengths and experimentally observed rate constants [Nature 2001, 412, 318] were found to be consistent such that, up to n = 2, the exponential decrease of the rate constants is associated with the donor-acceptor coherence driven charge transfer. In contrast, the rate constants become insensitive to the distance for n > or = 3 in which donor and acceptor are no longer significantly correlated. It was also found that the coherence within a collective state governs the overall charge transfer, which is composed of a part of a sequence within the coherence length from the donor.