The present document provides a method for determining transport block size (TBS), a base station and a terminal, including: a terminal receives downlink control signaling transmitted by a base station, obtains a combination of I′TBS and N′PRB, {ITBS, N′PRB}, and selects a mapping way to determine transport block size according to {I′TBS, N′PRB}, wherein, the mapping way includes at least one of following rules: a first rule, using high-layer TBS to obtain low-layer TBS according to I′TBS, N′PRB}; a second rule, obtaining TBS according to the {I′TBS, N′PRB} and a mapping relationship table pre-created; a third rule, determining a mapping factor according to the {I′TBS, N′PRB}, obtaining {ITBS, NPRB} according to the {I′TBS, N′PRB} and mapping factor, then determining TBS according to the {ITBS, NPRB} and a related {ITBS, NPRB} and TBS mapping relationship table, wherein the mapping factor is a real number greater than 0.