The common setting calculation of microcomputer-based current instantaneous trip protection results in the circuitry without extent of protection sometimes, then bring about jump the over trip when occur short circuit faults of circuitry. For the line of 6 kV is short in underground mine, besides the sensitivity and extent of protection are affected by operation mode and fault type of power system directly. According to the existing problems, a new method that the operation mode of electric power system is able to be identified automatically with adaptive technique was used, which can change the set point auto-turning and the characteristic of protection, through the surveillance and analysis to voltage and current of each line with real time, and it is not necessary to judge fault type as phase faults protection, which makes the function of microcomputer current instantaneous trip protection relays is always best, it could provide technical source for improving safety power supply in mine.