The invention relates to an adsorbent for separating bicyclo-arene in diesel oil. The adsorbent is characterized by comprising a low silica-alumina ratio LSX molecular sieve and two metal ions loaded on the vector. The grain size of an X molecular sieve and LSX is 50-200 nm. During the preparation of the adsorbent, water glass, sodium metaaluminate, sodium hydroxide, potassium hydroxide and deionized water are evenly mixed to form silicon-aluminum sol, the silicon-aluminum sol is aged and crystallized to form the molecular sieve vector, and the molecular sieve vector is in contact with mixed solution containing two metal ions to undergo ion exchange, so as to obtain the adsorbent. The adsorbent has high capability of absorbing bicyclo-arene, can effectively adsorb and separate bicyclo-arene in the diesel oil, and is high in selectivity.