The ternary strategy has been proven to be an effective method to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). In this work, a new non-fullerene fused-ring acceptor (BTMe-8Cl) with 3,8-dimethylbenzo[b]benzo[4,5]thieno[2,3-d]thiophene (BTMe) core and all chlorination end-group (4,5,6,7-tetrachloro-1H-indene-1,3(2H)-dione) is synthesized and incorporated as a guest electron acceptor in PM6:Y6:BTMe-8Cl ternary system. The addition of BTMe-8Cl effectively improves the open-circuit voltage (VOC) of the ternary OSCs due to the higher lowestunoccupied molecular orbital (LUMO) energy level of BTMe-8Cl than that of Y6. Fine-tuning the proportion of BTMe-8Cl in ternary OSCs results in the optimal phase separations in the ternary films. Finally, an excellent PCE of 18.39 % and a VOC of 0.896 V are achieved for the ternary OSCs based on PM6:Y6:BTMe-8Cl (1:1.2:0.2). Especially, the VOC of 0.896 V is the highest value for PM6:Y6 system up to now.