A power system of an electric vehicle, an electric vehicle comprising the same and a method for heating a battery group of the electric vehicle are provided. The power system comprises: a battery group; a battery heater, in which the battery heater comprises a output power adjusting module configure to adjust a heating power of the battery heater by adjusting a charge current and/or a discharge current; a battery management device configured to control the output power adjusting module to adjust the heating power of the battery heater to heat the battery group according to a temperature of the battery group when the temperature of the battery group is lower than a first heating threshold and a residual electric quantity of the battery group is larger than a parking electric quantity threshold; a motor controller connected with a motor and an electric distribution box respectively; and an isolation inductor.