The invention belongs to the technical field of silica preparation, and particularly relates to precipitated silica for low-viscosity toothpaste and a preparation method of the precipitated silica. The preparation method comprises the following steps: S1, adding a sodium sulfate solution to a reaction kettle, conducting stirring and heating, and then adding a sodium silicate solution to adjust thepH value; S2, simultaneously adding a sodium silicate solution and a sulfuric acid solution for reaction, and controlling the pH value of the reaction process to be 9-10, and after the sodium silicate solution is completely added, continuing adding the sulfuric acid solution until an end point pH value, and conducting stirring to obtain a preliminary product of silica; and S3, subjecting the preliminary product of silica to pressure filtration and washing by dilute sulfuric acid, and then conducting drying, and finally conducting crushing, so as to prepare the silica. The silica of the present invention can reduce the initial viscosity of the toothpaste and inhibit the viscosity of the toothpaste from growing, enables the toothpaste to maintain a proper viscosity, a good pseudoplasticityand thixotropy, and has a good application effect.