The invention provides a lithium ion battery positive electrode material and a preparation method of a precursor thereof. The preparation method comprises the steps of adding a salt solution and an alkali solution containing an aluminum element and ammonia water into a reaction kettle with an overflowing hole for reaction, performing solid-liquid separation, washing, drying and sieving on precursor paste obtained by overflowing so as to obtain a precursor uniformly doped with aluminum, mixing the precursor and a lithium source, and performing sintering, breaking and sieving to obtain the positive electrode material uniformly doped with aluminum. By the method, uniform doping of the aluminum element can be achieved, the process is simple and is easy and stable to control, and the method islow in production cost and is suitable for industrial production on a large scale.