<p>Using a low-noise static load experimental system, an electric–seismic signal strength measurement experiment involving the static load failure of water injection samples was carried out. A force–electricity coupling model was derived for water injection samples under load damage on the basis of damage mechanics and the statistical theory of coal–rock strength. The results showed that the structure of samples softened after immersion in water, the compressive strength decreased, the peak strain increased, and the impact proneness decreased. The sample shifted from single-shear damage to tensile–single-shear or multishear damage, the crack area increased, and the crack area growth rate decreased. With increasing water content, the maximum reductions in the electromagnetic signal strengths of the water injection samples under uniaxial loading and cyclic loading were greater than 40% and 70%, respectively. The energy value carried by the electromagnetic signal decreased, and the growth of the cumulative energy value slowed in the time domain. The electric–seismic signal strength generated by cyclic loading failure of a sample was one order of magnitude greater than that generated by uniaxial loading. The test results showing the anti-impact effect of coal seam water injection in a mine revealed that the optimum water injection interval of the water injection sample was 7.8–9.7%, and the optimal water injection interval for the sample was in line with the test standard for the water injection coal seam anti-impact effect. This research provides theoretical support for the monitoring and early warning of pressure bumping in water injection coal seams.</p>