A leakage current sensor, comprising: an input end, an output end, and an ASIC chip, wherein the ASIC chip is electrically connected with the input end for reading analog quantity signals of the input end, wherein the ASIC chip is further electrically connected to a digital signal processing module, wherein the digital signal processing module is configured to output digital quantity signals to the output end, wherein the input end comprises a current sampling unit, wherein the current sampling unit is used for sampling and acquiring an analog quantity of a reference current or a leakage current, characterized in that: the digital signal processing module is configured to simultaneously feedback the output digital quantity signals to the ASIC chip, thereby forming a closed-loop feedback circuit, and a reference unit is arranged between the current sampling unit and the ASIC chip, wherein the ASIC chip is configured to control the reference unit to generate reference currents with different grades; wherein the ASIC chip is configured to repeatedly set a same reference current value for calibration, and to read digital quantity signals fed back by the digital signal processing module, thereby forming a corresponding mapping between the analog quantity and the digital quantity of the reference current; the ASIC chip is configured to compensate the errors of the analog quantity signals of the leakage current according to aforesaid corresponding mapping, thereby outputting digital quantity signals; and the ASIC chip has a preset programmable circuit which is programmed to achieve an accurate gain output of the digital quantity signals. an input end, an output end, and an ASIC chip, wherein the ASIC chip is electrically connected with the input end for reading analog quantity signals of the input end, wherein the ASIC chip is further electrically connected to a digital signal processing module, wherein the digital signal processing module is configured to output digital quantity signals to the output end, wherein the input end comprises a current sampling unit, wherein the current sampling unit is used for sampling and acquiring an analog quantity of a reference current or a leakage current, characterized in that: the digital signal processing module is configured to simultaneously feedback the output digital quantity signals to the ASIC chip, thereby forming a closed-loop feedback circuit, and a reference unit is arranged between the current sampling unit and the ASIC chip, wherein the ASIC chip is configured to control the reference unit to generate reference currents with different grades; wherein the ASIC chip is configured to repeatedly set a same reference current value for calibration, and to read digital quantity signals fed back by the digital signal processing module, thereby forming a corresponding mapping between the analog quantity and the digital quantity of the reference current; the digital signal processing module is configured to simultaneously feedback the output digital quantity signals to the ASIC chip, thereby forming a closed-loop feedback circuit, and a reference unit is arranged between the current sampling unit and the ASIC chip, wherein the ASIC chip is configured to control the reference unit to generate reference currents with different grades; wherein the ASIC chip is configured to repeatedly set a same reference current value for calibration, and to read digital quantity signals fed back by the digital signal processing module, thereby forming a corresponding mapping between the analog quantity and the digital quantity of the reference current; the ASIC chip is configured to compensate the errors of the analog quantity signals of the leakage current according to aforesaid corresponding mapping, thereby outputting digital quantity signals; and the ASIC chip has a preset programmable circuit which is programmed to achieve an accurate gain output of the digital quantity signals.