A method for improving the particle size and morphology of a neutralizing agent used in the laterite nickel ore hydrometallurgy, in a process flow for producing nickel-cobalt-manganese hydroxide by the laterite nickel ore hydrometallurgy, a nickel-cobalt-manganese-containing feed liquid is subjected to one-stage iron-aluminum removal treatment and two-stage iron-aluminum removal treatment by using a neutralizing agent successively, wherein the -200 mesh sieving rate by mass ratio of the neutralizing agent is 85%-90%, and the spherical coefficient of solid particles of the neutralizing agent is not less than 0.6. In the disclosure, the particle size and morphology of the neutralizing agent are respectively improved so as to be used in the steps of one-stage iron-aluminum removal treatment and two-stage iron-aluminum removal treatment. The iron-aluminum removal rates in the steps of one-stage iron-aluminum removal treatment and two-stage iron-aluminum removal treatment can be effectively increased, and at the same time, the surface roughness of the solid particles of the neutralizing agent can be ensured to be lower, thereby reducing the rates of nickel, cobalt, and manganese ions reacting with local alkali to generate precipitations, thereby reducing the loss of nickel, cobalt, and manganese and further improving the yield of nickel-cobalt-manganese hydroxide produced by the laterite nickel ore hydrometallurgy.