The invention relates to the technical field of functional building paint and provides a preparation method of negative ion basic paint. The preparation method comprises the following steps of adding deionized water and a part of auxiliary agents into a high-speed dispenser, carrying out low-speed stirring, wherein the part of auxiliary agents comprise other auxiliary agents but an antifoaming agent, adding a negative ion additive, a pigment and a filler into the high-speed dispenser, carrying out high-speed stirring to obtain slurry, adding a synthetic resin emulsion and the rest of the auxiliary agents into the slurry, carrying out low-speed stirring dispersion, and carrying out filtration by a screen mesh to obtain the negative ion basic paint. The negative ion basic paint can be used as a main raw material for preparation of negative ion texture paint and is a novel paint component product. Through use of the negative ion additive in the negative ion basic paint, the film of the coating product has a negative ion continuous-release function, can be used in occasions of residential buildings, commercial buildings and common buildings and has a wide application prospect. The preparation method has simple processes, is convenient and is conducive to reduction of an industrial production cost.