Three-dimensional hierarchical porous carbon materials with flower-like superstructures are of great interest for energy applications since their unique shape not only provides high accessible surface area and consequently more exposed active sites but also facilitates ion transport for high-rate capability. However, finding a controllable way to make porous carbons with such specific shapes has been challenging. Herein, we report a tunable and simple method for one-pot synthesis of polyacrylonitrile and its copolymer nanostructured particles with various superstructures (flower, pompom, hairy leave, and petal shapes) controlled by employing various solvents or by the incorporation of different co-monomers. The correlation between polymer particle shapes and solvent properties has been identified through Hansen solubility parameters analysis. The obtained uniform polyacrylonitrile particles could be readily converted into porous carbons by high-temperature gas treatment while maintaining the original shape of the polymer precursor structures. The resulting carbon materials have high nitrogen-doping concentration (7-15 at%) and tunable porous structures. This novel synthetic method provides a simple way to make porous carbons with controllable morphology and potentially advantageous properties for a variety of potential energy and environmental applications, such as electrochemical energy conversion and wastewater treatment.