Considering its potential application in improving the performance of a single-molecule biosensing device, the diffusiophoresis of a polyelectrolyte sphere in a charged cylindrical nanochannel is studied taking account of the effect of diffusioosmosis flow. The interaction of the double layers in the present system is expected to influence significantly the relevant fields, yielding profound diffusiophoretic behaviors. Adopting a zwitterionic, pH-regulated polyelectrolyte in a silicon dioxide nanochannel as an example, these behaviors are simulated by varying the pH and the bulk salt concentration of the liquid phase, and the nanochannel radius. We show that the charged nanochannel could influence significantly both the quantitative and the qualitative behavior of the polyelectrolyte. The underlying mechanisms leading to this observation are discussed in detail.