Abstract: The paper introduced an anti-override trip system based on principle of zone protection, described basic idea and working process of zone protection technology and generating and control logic of blocking signal in details, and analyzed an example of power supply system of a coal mine. The analysis result shows that anti-override trip system based on principle of zone protection makes the relay protection of underground substation no longer rely on coordinate of fault current value and operating time, which can cut off fault quickly and accurately to achieve protection selectivity and improve protection level of underground substation.