The invention discloses a device for testing the anti-water-channeling performance of a cement paste. The device comprises a constant-temperature heating water tank, a low-speed circulation pump, a rotary viscometer, a water channeling simulation device and a sewage drain tank. The water channeling simulation device includes a cement paste cylinder for installing a tested cement paste; the cementpaste cylinder has a cylinder body having the bottom and a sandwich structure; a water inlet is formed in the lower part of the cylinder wall of the outer side of the cylinder body; and a drainage hole is formed in the upper part of the cylinder wall of the outer side of the opposite side. A plurality of simulation apertures for simulating aperture gaps of the stratum are formed in the cylinder wall of the inner side of the cylinder body. The water inlet is connected with the constant-temperature heating water tank by the low-speed circulation pump; and the drainage hole is communicated with the sewage drain tank. Constant-temperature simulated stratum water flows into the sandwich layer of the cylinder body through the water inlet and is discharged into the sewage drain tank via the drainage hole, thereby simulating flowing of the stratum water. The rotary viscometer is used for measuring the viscosity of the cement paste in the cement paste cylinder. Therefore, the anti-water-channeling performance of the cement paste can be measured accurately; and the experimental basis is provided for cement paste formulation adjustment.