The invention discloses a sample circuit of synchronizing signals of grid voltage. The sampling circuit comprises a power supply, a slide-wire rheostat, a first voltage comparator, a first resistor, a second resistor, a second voltage comparator, a third resistor, a fourth resistor, a fifth resistor and a triode, wherein a sliding end of the slide-wire rheostat is connected with a non-inverting input end of the first voltage comparator; an inverting input end of the first voltage comparator is connected to an output end of the first voltage comparator; an inverting input end of the second voltage comparator is connected with the output end of the first voltage comparator through the first resistor, and the non-inverting input end of the second voltage comparator is grounded through the second resistor, and an output end of the second voltage comparator is connected with the non-inverting input end of the second voltage comparator through the third resistor; and the base electrode of the triode is connected with the output end of the second voltage comparator through the fourth resistor, the emitter electrode of the triode is connected with the power supply, and the collector electrode of the triode is grounded through the fifth resistor. The sample circuit of the synchronizing signals of the grid voltage, provided by the invention, is simple in structure, low in cost and easy to implement, and by using the sample circuit, the precise zero crossing point detection can be achieved.