The invention provides a sodium-ion battery positive electrode material Na3V2(PO4)3/nitrogen-doped carbon synthesized based on organic phosphonic acid and a preparation method. The preparation methodcomprises the steps of firstly, adding a proper amount of deionized water into organic phosphonic acid and a sodium source, stirring and dissolving to obtain a clear solution A, and dissolving a vanadium source to obtain a clear solution B; adding the solution B into the solution A to form a mixed solution C; heating and stirring the mixed solution C at the temperature of 80-100 DEG C until moisture is evaporated to dryness, and putting the obtained gelatinous substance into a drying oven for drying at a temperature of 80-100 DEG C for 5-12 hours; and grinding the obtained solid, and carryingout secondary sintering under the protection of argon to obtain the product. The organic phosphonic acid has multiple functions, that is, the organic phosphonic acid not only serves as a source of phosphonate radicals in Na3V2(PO4)3, but also serves as a nitrogen source and a carbon source. Compared with the existing method, the preparation method is simple, easy to control and low in cost, and the prepared Na3V2(PO4)3/nitrogen-doped carbon has high specific capacity and good cycling stability and rate capability.