A method for reconnecting a relay in a vehicle battery management system includes: measuring an insulation resistance between a positive electrode or a negative electrode of a battery and a vehicle chassis; turning off each of relays connected between the positive and negative electrodes of the battery and a load when the measured insulation resistance is less than a reference value; re-measuring the insulation resistance; and performing a relay-on sequence for turning on each of the relays when the resistance value of the re-measured insulation resistance is greater than the reference value. A relay reconnection number of the relay-on sequence, based on a repetition of the measuring and re-measuring, is set and limited so as to not exceed a threshold value.