Rational manipulation of the carbon framework from the microporous to nonporous via a molecular design approach is interesting but challenging. Herein, we report a versatile strategy for transforming the microporous carbon framework to the low porous one by an elaborate molecular crosslinker design in the polystyrene (PS) precursor. Direct coupling of benzene rings in PS via Scholl reaction yields hypercrosslinked PS-derived carbon with low porous framework, while insertion of methylene crosslinker into PS via a solvent knitting strategy leads to microporous carbon framework. The results show that methylene crosslinker functions as molecular-scale soft templates for facilitating micropores, whereas direct linking PS chains promotes aromatization and mitigates micropore formation during the pyrolysis. The distinct carbon frameworks derived from similar precursor and pyrolysis condition provide an intriguing platform for structure-property relationship study, as preliminarily exemplified by the application in Na ion storage. The low-porosity carbon shows higher initial Coulombic efficiency and superior capacity thanks to its low surface area and enhanced Na insertion into pseudo-graphitic microcrystal structure. The present protocol opens up new avenues towards flexible carbon framework porosity manipulation at molecular level and would trigger further efforts for low-porosity carbons in energy storage.