Accurately and rapidly analyzing the ionic current/conductance in a nanochannel, especially under the condition of overlapped electric double layers (EDLs), is of fundamental significance for the design and development of novel nanofluidic devices. To achieve this, an analytical model for the surface charge properties and ionic current/conductance in a pH-regulated nanochannel is developed for the first time. The developed model takes into account the effects of the EDL overlap, electroosmotic flow, Stern layer, multiple ionic species, and the site dissociation/association reactions on the channel walls. In addition to good agreement with the existing experimental data of nanochannel conductance available from the literature, our analytical model is also validated by the full model with the Poisson-Nernst-Planck and Navier-Stokes equations. The EDL overlap effect is significant at small nanochannel height, low salt concentration, and medium low pH. Neglecting the EDL overlap effect could result in a wrong estimation in the zeta potential and conductance of the nanochannel in a single measurement.