The invention relates to the technical field of oil production of oil fields, and discloses a calculating method of the recovery efficiency under a secondary-tertiary combined development mode. The method comprises the steps that the water flooding sweep coefficient E and the oil displacement efficiency E of primary oil production are obtained; secondary development water flooding is carried out under the primary oil production injection condition, and the water flooding sweep coefficient percentage omega increased by the secondary development water flooding is obtained; tertiary oil production is directly carried out under the primary oil production injection condition, and the sweep coefficient percentage epsilon increased by the tertiary oil production and the oil displacement efficiency E of the tertiary oil production are obtained; a calculation model of the sweep coefficient E under the secondary-tertiary combined development mode is established according to E, omega and epsilon; and the increment [delta]E of the recovery efficiency under the secondary-tertiary combined development mode relative to the recovery efficiency of primary oil production is calculated. The determined recovery efficiency increment [delta]E achieves the advantage of the integrity of a secondary development water flooding well network and the advantage of improving the oil displacement efficiency of the tertiary oil production, and the method can be used for theoretically understanding the recovery efficiency increasing value under the secondary-tertiary combined development mode.