The invention discloses a preparation method of a lithium manganate positive electrode material for a lithium ion power battery and the lithium manganate positive electrode material for the lithium ion power battery. The preparation method includes the steps: (1) simultaneously dropping sodium hydroxide solution and soluble manganese salt solution containing doped metal ions into electrolytic manganese dioxide suspension liquid under stirring conditions, and leading in air for oxidizing reaction while dropping to generate spherical doped manganese dioxide; (2) mixing the spherical doped manganese dioxide obtained in the step (1) with a lithium source, and sintering and crushing mixture to obtain a spherical doped lithium manganate precursor; (3) roasting and crushing the spherical doped lithium manganate precursor obtained in the step (2) in oxidizing atmosphere to obtain the lithium manganate positive electrode material for the lithium ion power battery. The prepared lithium manganatepositive electrode material for the lithium ion power battery has the advantages of high-temperature performance, excellent storage performance, stable structure, small specific surface area, low cost and the like.