In this paper, Poisson-Boltzmann equation and Navier-Stokes equation will be solved by Homotopy Perturbation method (HPM). Working fluid in this paper is assumed to be non-Newtonian which follows power law model. Zeta potential that is used for the potential in near wall area of a tube will be small enough in order to use some simplifications. In this paper, Poisson-Boltzmann equation for a 30 nm diameter nanotube with large zeta potential has been solved by Homotopy Perturbation Method (HPM). According to the literature, results have been compared with numerical solutions and consistency of the results has been considered. Results show that HPM can approach to this problem reliably.