Abstract: For problems that response time of underground integrated protection switches is long and uncertain because the switches are coming from different manufacturers and have different models, the paper proposed an improved protection scheme based on analysis of traditional protection scheme of zone selective interlocking: connect switch lockout signal interface of intelligent control module in tripping signal circuit of integrated protection switches in series, use 1:1 Hall-type current sensor to obtain current signal from secondary side of current transformer of the original protective device, and take the signal as acquisition signal of the intelligent control module. The scheme detects fault current through current sensor directly, which avoids protection from impact of integrated protection switches. The testing result shows that the intelligent control module in the improved scheme has response time of 800 μs, response speed is significantly improved compared with the traditional scheme.