With the widespread usage of plastic products, more and more phthalic acid esters (PAEs) pollutants entered into the environment, and then pose a potential threat to the ecosystems and human. In this work, mesoporous cellulose biochar (MCB) was taken as the adsorbent, and five different carbon chain structural phthalic acid esters (PAEs; DMP, DEP, DBP, DOP, DEHP) were selected as the adsorbates. The effects of CCS on the PAEs adsorption behaviors and mechanisms were systematically studied by the combination of experiments and molecular dynamics simulation. The adsorption capacity order of the five PAEs was as follows: DOP (74.42) > DMP (69.58) > DEP (68.91) > DBP (67.32) > DEHP (61.87). The adsorption processes were mainly driven by chemisorption. Therein, MCB adsorbed DMP, DEP, and DBP mainly through pi-pi electron-donor-acceptor (EDA) interaction, adsorbed DOP by the collaboration of hydrophobic and pi-pi EDA interactions, and adsorbed DEHP mainly via hydrophobic interaction. For the short carbon chain PAEs, the mainly adsorption mechanisms of PAEs onto porous biochar were pi-pi EDA interaction and pore-filling. With the increase of carbon chain length, the pi-pi EDA interaction and pore-filling would weaken, thus the hydrophobic interaction would enhance contrastingly. Owing the same carbon number of the carbon chain, the branched structure would accelerate the agglomeration of adsorbate molecules and weaken the adsorption force. Therefore, the current study could provide strategies for the preparation of highly effective biochar adsorbents, and improve selective adsorption efficiency of PAEs.