The distribution and magnitude of the shear stress at the interface between the grout of a compression anchor rod and rock are strongly affected by the Poisson effect. To quantitatively analyze the influence of the Poisson effect on the interfacial shear stress of compression anchor rods, the equations for calculating the axial force and interfacial shear stress at the grout cross section in the anchorage section are derived in this paper, accounting for the Poisson effect of the grout. Based on the analytical solution, a new equation of the influence coefficient of the Poisson effect is proposed to quantitatively evaluate the influence of the Poisson effect on the interfacial shear stress. Distributions of the interfacial shear stress and the influence coefficient of the Poisson effect are analyzed with different parameter values. There is a neutral point in the anchorage section near the bearing plate, at which the magnitude of the shear stress is not affected by the Poisson effect. When the Poisson effect is considered, the interfacial shear stress from the neutral point to the bearing plate increases, and the distribution curve becomes steep. However, the interfacial shear stress far from the neutral point is low, and the distribution curve becomes smooth. Overall, the Poisson effect leads to a more nonuniform distribution of the shear stress at the interface of the compression anchor rod. A larger Poisson's ratio, smaller elastic modulus, and smaller diameter of the grout lead to a greater influence of the Poisson effect. Furthermore, a larger elastic modulus of rock leads to a greater influence of the Poisson effect. The Poisson's ratio of rock and that of grout both affect the Poisson effect greatly, but the influence of the variation in the Poisson’s ratio of rock on the Poisson effect is negligible. A larger interface friction angle leads to a greater influence of the Poisson effect.