In this study, impurity-free porous graphene (PG) with intrinsic pore structure was synthesized through a facile acid-alkali etching-assisted sonication approach. The pore structure appears on the surface of graphene sheets due to intrinsic defects of graphene. The PG possessed an extremely high specific surface area of 2184 m2/g, the size of～5μm and layer numbers of 3–8. Additionally, PG contained micropores and mesopores simultaneously, with an average pore diameter of approximately 3 nm. The effects of acid, alkali, and ultrasound treatment on PG preparation were elucidated by transmission electron microscopy and fourier transform infrared spectroscopy. First, in an acidic solution, oxygen-containing functional groups (hydroxyls, carboxyl, and epoxides) were formed due to the hydrolysis of sulfate and continuous transformations of these functional groups on graphene oxide. Second, under the synergistic effects of alkali and ultrasound treatment, PG was obtained due to the loss of carboxyl and epoxide groups. A new route for preparing PG was provided by the proposed method.