The invention discloses a high-voltage electrode material and a preparation method for in-situ coating of tin antimony oxide on the surface of cobalt lithium fluorophosphate and its application in lithium secondary batteries. It is characterized in that the prepared method comprises the following steps: weighing a certain amount of cobalt lithium fluorophosphate precursor into a beaker, adding a dispersant, adding an antimony source and a tin source according to a certain mass ratio, dissolving in the dispersant, and adding an excessive amount of Precipitating agent, precipitating, centrifuging, washing, after the precursor is calcined and reacted in situ, the lithium cobalt fluorophosphate cathode material coated in situ with tin oxide and antimony is obtained. The lithium cobalt fluorophosphate cathode material coated with antimony tin oxide in situ prepared by this method has good crystallinity, good dispersion, uniform coating, high discharge platform and high energy density, and exhibits excellent electrochemical performance. The performance, especially after many charge-discharge cycles, still maintains a high discharge specific capacity and energy density, which will help further research and application of high-voltage and high-energy-density cathode materials.