The rheological properties is an important basis for the design of grouting parameters in geological disaster management. Rheological property of cement suspension is affected by many factors, and its mechanism is uncharted. In this study, the influence of particle size distribution on rheological property is analyzed. The focused beam reflectivity measurement system was used to measure the chord size and number of flocculated particles under different water-cement ratio, cement fineness and shear rate, and the rheological properties of slurry under the same conditions were measured. The effects of particle size distribution on rheological properties were analyzed. The results show that with the increase of water-cement ratio, cement fineness and shear rate, the chord size of flocculated particles decreases and the number of particles increases. The degree of particle flocculation increased linearly with the increase of time. The yield strength and molding viscosity decrease with the increase of water-cement ratio, and increase with the increase of cement fineness. The apparent viscosity decreases with the increase of shear rate and shows a reversible change. The change of flocculation structure is consistent with the change of rheological properties. The water-cement ratio, cement fineness and shear rate affect the rheological properties by influencing the flocculation structure. This study reveals the change of rheological properties from the perspective of flocculation structure, which can provide guidance for the design and application of cement grout.