The invention discloses a method for calculating the oil filling amount of a capsule oil filling pressure-bearing type acoustic logging instrument. The method comprises the following steps: (1) separately acquiring a stratum parameter and an oil parameter used in a capsule, wherein the stratum parameter comprises a stratum temperature gradient Gt, a stratum pressure gradient Gp, a surface constant-temperature belt depth h0 and a surface constant-temperature belt temperature tc, and the oil parameter comprises an oil volume heat expansion coefficient alpha and an oil volume elasticity modulus k; (2) calculating volume change rate delta Vt of oil used in the capsule in a specific stratum depth by formula as shown in specification; and (3) at the room temperature and under a barometric pressure, setting the volume of the oil which can be accommodated in the capsule as V0 to obtain the oil filling amount which is V0.(1-delta Vt, P). By the calculating method, the oil filling amount can bequantitatively calculated and adjusted according to geological parameters of different oil regions, excessive expansion of the capsule is prevented, and therefore, the reliability of the instrument isimproved.