The invention discloses a working status monitoring circuit and method of a secondary neutral point valve piece of a voltage transformer. The occurrence of secondary valve piece grounding phenomenon and secondary circuit insulation breakdown phenomenon of the voltage transformer are avoided by using the working status monitoring circuit and method. The working status monitoring circuit includes avoltage transformer (1), a control room N600 miniature busbar one spot grounding point (3), an alternating current relay, a direct current relay, a main zinc oxide valve piece (7), a spare zinc oxidevalve piece (9), a direct current working power supply (11) and an alarm signal generator circuit (15), a protection circuit (2) is connected with a secondary winding of the voltage transformer (1), aneutral point N (4) of the secondary winding of the voltage transformer (1) is electrically connected with the control room N600 miniature busbar one spot grounding point (3) through a N600 miniaturebusbar special connecting line (5). The switching between a main zinc oxide valve 7 and a standby zinc oxide valve 9 is achieved through the combination of a constant open contact point and a constant close contact point of the alternating current relay and the direct current relay. The probability of occurrence of power grid accidents due to relay protection misoperation and rejection is reduced.