The present disclosure relates to the field of battery technology, and particularly, to a positive plate and a preparation method thereof, and a sodium-ion battery. The positive plate includes a current collector and at least one cathode material layer provided on at least one side surface of the current collector. The at least one cathode material layer includes a layered transition metal oxide and a polyanionic compound. A mass ratio of the layered transition metal oxide to the polyanionic compound is 2+1ρ1/ρ2∼42+1ρ1/ρ2, wherein ρ1 indicates a true density of the layered transition metal oxide, ρ2 indicates a true density of the polyanionic compound, and 1.25≤ρ1/ρ2≤1.86. A particle size distribution of the layered transition metal oxide satisfies: 3−2D50≤D10≤2−1D50, and a particle size of the polyanionic compound satisfies: D′50≤2−14D50. The positive plate of the present disclosure may have effectively improved air stability, and also higher compaction density and excellent electrochemical performance.