The invention relates to a method for preventing power grid distance protection maloperation caused by voltage-losing after start-up. The method is used for judging whether voltage transformer disconnection occurs or not within a certain time frame after starting a distance protection apparatus in a power grid so as to prevent maloperation. The method is as follows: if continuous n sampling points satisfy the following criteria: (1), voltage break variable of any one phase is greater than a preset voltage leap threshold value; (2) three-phase voltages calculated by a half-cycle algorithm are all less than 2V; (3), three-phase current break variables within 20 ms are all greater than a starting constant value of the distance protection apparatus; and (4), a zero-sequence current or a negative-sequence current is greater than a set current threshold value, judging whether the voltage transformer disconnection occurs or not within a certain time frame after unsymmetrical faults out of a positive direction region; and preventing the maloperation of the distance protection apparatus according to the judgment result. Through the method, whether the voltage transformer disconnection occurs consecutively or not within a short time after the distance protection apparatus is started due to unsymmetrical faults out of the positive direction region so as to further avoid the distance protection maloperation.