The invention belongs to the field of lithium-ion batteries and provides a positive electrode material LiCo<1-x-y>VMgO<2-y>F of a lithium-ion battery and a preparation method of the positive electrode material LiCo<1-x-y>VMgO<2-y>F for overcoming the disadvantage that the positive electrode material layered lithium cobalt oxide (LiCoO2) of the lithium-ion battery is relatively poor in electrochemical properties. A molecular expression of the positive electrode material of the lithium-ion battery is LiCo<1-x-y>VMgO<2-y>F, wherein x is smaller than or equal to 0.05 and greater than 0; and y is smaller than or equal to 0.03 and greater than 0. The positive electrode material LiCo<1-x-y>VMgO<2-y>F of the lithium-ion battery is obtained by replacing an oxygen element with a fluorine element and replacing a cobalt element with vanadium and magnesium elements; and charging and discharging can be carried out at 4.5V voltage. One part of oxygen element is replaced with a small amount of negative monovalent fluorine element, so that the comprehensive electrochemical properties of the material are greatly improved; in a room-temperature environment, when the constant-current charge-discharge rate is 0.5C and the charge-discharge cut-off voltage is 2.7V-4.5V, the initial specific discharge capacity of the positive electrode material, of a layered structure, of the lithium-ion battery can be 179.5mAh/g and can still be 157.5mAh g<-1> after 50 cycles; and the capacity retention ratio is 87.7%. Meanwhile, the preparation technology is simple to operate, large-scale industrial production is easy to implement and the repeatability is high.