The invention discloses an electric vehicle, a battery management system and a failure detection method thereof. The method includes steps of controlling balance units corresponding to battery individuals in a switching-off state and acquiring a first voltage sampled by a sampling unit corresponding to an i battery individual and acquiring a second voltage sampled by a sampling unit corresponding to an i+1 battery individual; controlling a balance unit corresponding to the i battery individual to switch on and acquiring a third voltage sampled by a sampling unit corresponding to the i battery individual and acquiring a fourth voltage sampled by a sampling unit corresponding to the i+1 battery individual; according to the first voltage, the second voltage, the third voltage, the fourth voltage and the current of a balance circuit corresponding to the i battery individual, calculating a connection resistance between the i battery individual and the balance unit corresponding to the i battery individual; generating early warning information when a change rate of the connection resistance is greater than a preset threshold value and thus sending the early warning information at the initial stage of wiring harness connection reliability deterioration.