The quality of covalent organic frameworks (COFs) crucially influences their mechanistic research and subsequent practical implementations. However, it has been widely observed that the structure damage induced by the activation procedure could compromise the quality of COFs. Here we develop a self-sacrificing guest method for synthesizing high-quality two-dimensional COFs (SG-COFs) by incorporating salt guests into the pores of the COF structure. These introduced salts play an indispensable role in supporting COF pores and mitigating quality loss during the activation process. Interestingly, due to the unique characteristic of salts decomposing into gases upon heating, this method can ultimately enable the synthesis of highly pure, high-quality COFs without the presence of residual guest molecules. The resulting sixteen COFs display superior crystallinity and porosity compared to those synthesized using conventional routes. Moreover, these high-quality SG-COFs have demonstrated to be highly efficient adsorbents for removal of per- and polyfluoroalkyl substances.