The invention relates to a digital gas protection method for a transformer on-load oil tap-changer; a flow velocity sensor is arranged in an oil conservator connecting pipe, and oil flow velocity information is transmitted to a gas relay in real time; the oil flow velocity information in the oil conservator connecting pipe of the on-load oil tap-changer is measured through the oil flow velocity sensor, and when the oil flow velocity is greater than an instantaneous action value, a relay acts; otherwise, the oil flow velocity is compared with a fixed time tag protection constant value, if the oil flow velocity is larger than the fixed time tag protection constant value, timing is carried out, if the time reaches 200 ms, the gas relay acts, a next turn of oil flow velocity information judgement is carried out if not reaching 200 ms, and if the oil flow velocity is smaller than or equal to the fixed time tag protection constant value, the timer is reset and carries out the next turn of oil flow velocity information judgement. According to the method in the invention, a quick motion can be carried out when the oil flow velocity is large; when it cannot be judged whether being a fault only through the oil flow velocity information, a malfunction of gas protection due to too large oil flow velocity caused by the on-board oil tap-changer normal switch process is avoided through time delay setting.