A power system of a hybrid electric vehicle, a hybrid electric vehicle comprising the same and a method for heating a battery group of the hybrid electric vehicle are provided. The power system includes: a battery group; a battery heater connected with the battery group; a battery management device configured to control the battery heater to heat the battery group with a first power or a second power when the hybrid electric vehicle is in an electric vehicle mode or a hybrid electric vehicle mode, 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; an electric distribution box; an engine; a motor; a motor controller connected with the motor and the electric distribution box respectively; and an isolation inductor.