The invention discloses a hydraulically-operated mechanical digital lock, comprising a digital cylinder and a digital key; the digital cylinder is composed of executing cylinders 11, a code change member 3, a plurality of base hole seats 4, a plurality of decoding members 5, a plurality of return members 6, a plurality of elastic parts 7, a fluid 12 and the like; the digital key is composed of a plurality of input members 11 and an input basic member 10; decoding of the lock, namely passing conditions of the fluid 12, is expressed through an ordered combination of positions of the decoding members 5 so that action conditions of the executing cylinders 1, namely unlocking conditions, are expressed; an input code is expressed through an ordered combination of the positions of the input members 11; unlocking is allowed when an unlocking code of the lock is in conformity with an input code of the key.