Research was conducted on the depth of the mining-induced failure zone in coal mine floors. Combined with theoretical analysis and field tests, the evolutionary law and actual depth of the zone were revealed. Theoretically, the mining-induced response of the floor was divided into four stages: in-situ stress equilibrium, mining stress disturbance, significant floor activation, and stress recovery and stabilization. Stress distribution models for each stage were derived. Based on the Mohr-Coulomb strength criterion and limit equilibrium theory, a plastic formula for the maximum failure depth of the floor was established, and a piecewise descriptive function of the failure depth with the advance distance of the working face was constructed, by which the dynamic evolution mechanism of the failure depth was clarified. In field tests, the borehole double-end sealing water leakage measurement method was adopted. Observation Hole A, Observation Hole B, and Contrast Hole A' were arranged in the auxiliary haulage roadway of the working face. The degree of fracture development was quantified through segmented sealing, constant-pressure water injection, and flow rate monitoring. The observation results showed that the difference in water leakage at different depths of Contrast Hole A' reflected the gradient of fracture development. The depths of the floor water-conducting zones at Observation Hole A and Observation Hole B were 17.6 m and 16.8 m, respectively, which verified the rationality of the theoretical model. Scientific basis was provided by this research for the evaluation of mine floor stability and the prevention and control of water inrush risks.