A method of designing left-handed metamaterials based on inter-unit-cell coupling was proposed in this paper. A theoretical model was established using equivalent circuit theory. By properly setting the geometrical parameters of adjacent unit cells, the electric resonance frequency can be made equal to the magnetic resonance frequency. Thus, the left-handed bandwidth reaches its maximum. A typical left-handed metamaterial based on inter-unit-cell coupling was fabricated and tested. The experimental results show that the test sample has equal electric and magnetic resonance frequencies and the left-handed bandwidth is 24 GHz. This verifies the design method proposed in this paper.