The balance of the series lithium ion battery can prevent the overcharge or over-discharge of some single cell in the battery group, so as to prolong the service life of the battery. Aiming at the current active equalisation circuit, it is difficult to achieve equalisation of any single cell in battery pack based on a small number of components. A new active equalisation circuit with balanced power supply is proposed. The circuit is composed of the current mainstream switch array, bidirectional DC-DC converter and balanced power supply. The switch array is divided into two groups, the first group has N+1 switches, in which N is the number of series batteries, which provides access for the balanced single cell battery; the second group has 4 switches and is divided into two groups to achieve the purpose of controlling the polarity of the bidirectional DC-DC circuit. By controlling the switching array and the working state of the bidirectional DC-DC converter, the energy exchange between the single cell and the balanced power supply in the battery group is realised, and then the target of the battery pack is balanced. The balanced power supply can also provide power for load to reduce battery load under the condition that the load needs more power. On this basis, we use MATLAB/SIMULINK software to build the model and simulate it. The simulation results show that, under the premise of using less components (N+1+4 switches and one bidirectional DC-DC converter), the structure can achieve a balanced target for any single cell in the battery group, which proves that the circuit can meet the requirements well.