The functional carbon nanotubes(CNTs) under different acid treatment conditions are systematically characterized with Boehm’s titration method and the N2 adsorption method using high-resolution transmission electron microscopy and specific surface area and pore size analyzer. The results show that the functionalized CNTs and pristine CNTs are characterized with aggressive meso-and large pores. Acid treatment increases the pore volume and specific surface area of these pores. The created functional groups jam the micropores and opened inner hollow pores. Such effect becomes drastically with the increasing of the amount of functional groups. The effects of total acid amount on specific surface area were also investigated and the optimal value is about 1 mmol·g-1.