The present disclosure provides a charging system, charging method, and charging control device. The charging system comprises a charger configured to be coupled to an external power source with its one end; a plurality of secondary batteries configured to be coupled to the charger, respectively; and a control device configured to be coupled to the charger and the plurality of secondary batteries, to control the charger to perform a charging operation on the plurality of secondary battery. According to the present disclosure, the secondary batteries having harmonics with identical frequencies and opposite phases are connected in parallel for charging, to reduce or eliminate the harmonic distortion generated by high order harmonics, and effectively reduce the value of THD.