A CT polarity testing device, which includes: a first resistor (R1), a second resistor (R2), a third resistor (RS), a diode (D), a relay (CJ), a first switch (AN1), a second Second switch (AN2), third switch (AN3), single pole double throw switch (K2), switch (K1), first DC power supply (EC1), second DC power supply (EC2), first light emitting diode (LED1) , the second light emitting diode (LED2). The invention fully meets the actual needs of the relay protection work site, has the characteristics of sensitive testing, convenient operation, portability, reliability and practicality, etc., can greatly improve the working efficiency of the site, and the test light indication is intuitive and specific, and the power consumption of electronic components is small , low cost, low energy consumption, and can be used for long-term testing.