Offset ink viscosity characteristics and the shear rate of printing process were analyzed. The viscosity of ink was measured through experiments and the viscosity of the ink transferred from blanket cylinder to paper was calculated. The same products were printed with different ink viscosities in same condition. The relationships between the ink viscosity and solid density, dot gain and the chrominance were discussed. The mechanism of the influence of ink viscosity on printing quality parameters was analyzed. The purpose was to provide reference for enterprises to use viscosity reducer reasonably.