The invention discloses a double-layer arrangement structure for electric main circuit equipment of an alternating current excitation variable-speed pumped storage unit. The electric main circuit equipment of the alternating current excitation variable-speed pumped storage unit is divided into alternating current excitation system equipment and variable-speed generator motor voltage loop equipment. The electrical main circuit equipment is arranged in a busbar hole, the busbar hole includes a double-layer structure of an upper layer of the busbar hole and a lower layer of the busbar hole, the upper layer of the busbar hole is provided with the alternating current excitation system equipment, and the lower layer of the busbar hole is provided with the variable-speed generator motor voltage loop equipment. The double-layer arrangement structure is clear and reasonable in arrangement structure and economical and practical; an underground main plant structure of a large-scale pumped storagepower station is not changed, and the difficulty of excavation support and engineering investment of an underground cavern group are greatly reduced; the structure is safe and reliable, and the operation and maintenance are convenient; and the temperature requirement of the cooling of an alternating current excitation power cabinet body and the operating environment of the electrical equipment ismet to ensure the electrical functions of the alternating current excitation system equipment and the variable-speed generator motor voltage loop equipment.