The invention discloses a preparation method of an all-gradient high-nickel ternary precursor and an all-gradient high-nickel ternary cathode material. The preparation method comprises the following steps: preparing a mixed solution A, a mixed solution B and a mixed solution C; performing parallel flow of the mixed solution A, an alkali solution and a complexing agent and pumping into a reaction kettle; continuously pumping the mixed solution B into the mixed solution A at the velocity of V1 after reaction time T1; continuously pumping the mixed solution C into the mixed solution B at the velocity of V2 after reaction time T2, thus realizing continuous progressive change of feeding materials and components of nickel salt, cobalt salt and manganese salt to obtain the all-gradient high-nickel ternary precursor; mixing a lithium source compound and the all-gradient high-nickel ternary precursor according to the molar rate to obtain a mixture; sintering the obtained mixture under an oxygenatmosphere; performing after-treatment after sintering to obtain the all-gradient high-nickel ternary cathode material. The preparation method disclosed by the invention is high in operability, easyto control, and can be used for industrial production; moreover, the obtained product has high content and is good in cycling stability.