In order to quantitatively examine the activation level for covalent‐organic frameworks (COFs) on gas adsorption, the effect of impurities on nitrogen uptakes in a series of boron‐based COFs was investigated by grand canonical Monte Carlo simulation (GCMC), based on accurate force fields derived from high‐level B2PLYP‐D3/def2‐TZVPP calculation. The conformations and the type of impurities were found to have little effect on the gas uptakes, but the quantity of impurities plays a crucial role on N2 loadings. More important, the terms of “activation mass ratio” and “activation volume ratio” were defined to estimate the realistic pore volume ratio for DBA‐COFs (DBA=π‐conjugated dehydro‐benzoannulene), and predict the potential of gas uptakes in DBA‐COFs. Our approach for DBA‐COFs materials could also be adopted for high‐throughput screening of a much vaster number of porous materials, to evaluate their impurities content and predict their adsorption potential.