The invention provides a detection device, a system and a method for the core wire grounding detection of a rail circuit. The detection device comprises an isolation resistor module, a sampling resistor and a power supply module which are sequentially connected in series. One end of the isolation resistor module is connected with one end of the sampling resistor. The other end of the isolation resistor module is used for being connected with a tested core wire, and the other end of the sampling resistor is connected with the power supply module. The detection device further comprises a collecting module, and the collecting module is connected with the sampling resistor in parallel. The collecting module is used for collecting voltage data at the two ends of the sampling resistor accordingto a preset rule. When the cable core wire of the rail circuit is not grounded, no current flows through the sampling resistor. At this time, the voltage applied across the two ends of the sampling resistor is zero. When the cable core wire is grounded, a voltage drop is generated on the sampling resistor. At this time, the collecting module is capable of collecting the voltage, so that the groundfault of the core wire of the rail circuit can be judged. Furthermore, corresponding measures can be taken in time and accidents are avoided. The driving safety is guaranteed.