The invention discloses a reduction-ratio-criterion-based magnetic field analysis method for a multi-encapsulated dry type air reactor. The method comprises the following steps that: a multi-encapsulated air reactor is simplified to be a single-layer-coil type single-encapsulated hollow air reactor; and a ring-shaped carrier conductor is used as an air reactor simplification model, different currents are led in each annular conductor and the turn numbers in the annular conductors are different, comparison is carried out and an optimized simplification model closest to the magnetic field distribution of the air reactor model is selected. Therefore, the spatial magnetic field analysis and prediction of large dry air reactor is realized; and the safe and reliable operation of the electric reactor and the power system is guaranteed.