Proton enhancement in an extended nanochannel is investigated by a continuum model consisting of three-dimensional Poisson-Nernst-Planck equations for the ionic mass transport of multiple ionic species with the consideration of surface chemistry on the nanochannel wall. The model is validated by the existing experimental data of the proton distribution inside an extended silica nanochannel. The proton enhancement behavior depends substantially on the background salt concentration, pH, and dimensions of the nanochannel. The proton enrichment at the center of the nanochannel is significant when the bulk pH is medium high (ca. 8) and the salt concentration is relatively low. The results gathered are informative for the development of biomimetic nanofluidic apparatuses and the interpretation of relevant experimental data.