A multiphysics model is presented to simulate the ionic transport interaction between the smart pH-electric-sensitive hydrogel and solution in micro-scale channel for BioMEMS application, when it is immersed into a pH buffer solution subject to externally applied electric field. It is called the multi-effect-coupling pH-electric-stimuli (MECpHe) model, and covers chemo-electro-mechanical coupled effect and the fixed charge density associated with the buffer solution pH and electric potential. The model enables us to predict the distributive diffusive ionic species concentrations and the distributive electric potential in both hydrogel and surrounding solution as well as the fixed charge density and the displacement of hydrogel, especially to study the ionic transport interaction between the soft smart hydrogel and solution in the micro-channel. By the MECpHe model, the equilibrium response of the smart hydrogels is simulated to the interaction with the solution pH and electric coupled stimuli. Influence of the several key parameters including the externally applied electric voltage and solution pH is discussed in detail on the distributions of ionic species concentrations and electric potential for the ionic transport systems in micro-scale channel.