The invention relates to a method for preparing high nickel-based ternary positive electrode precursor. The method comprises steps that first solution is prepared by using nickel salt, cobalt salt andmanganese salt as raw materials; sodium carbonate solution is prepared, and surfactant is added to the sodium carbonate solution and mixed uniformly to obtain second solution; the first solution andthe second solution are subjected to synthesis reaction to obtain a synthesis reaction product, and the synthesis reaction product is subjected to filtration, washing and drying to obtain the high nickel-based ternary positive electrode precursor; the synthesis reaction is carried out in a microchannel reactor.