The invention provides a variable-time limit distance protection ranging method for a power line and device. Firstly, through reactance line criteria under different fault conditions, a fixed value for each distance protection section is used as an initial setting impedance value, and a distance protection section for subsequent reactance line criterion is determined; then, according to a determined distance protection section setting impedance value calculation formula, a setting impedance value for next reactance line criterion for the distance protection section is determined; through multiple cycles, a final setting impedance value is determined; and finally, according to a distance calculation formula, the distance between a fault point and a protection mounting place in variable-timelimit distance protection is determined. According to the variable-time limit distance protection ranging method for the power line and the device provided in the invention, when fault of the power line happens in a distance protection section range, the fault point can be accurately positioned, and the error is 1e-3.