The invention provides a high-precision AD sampling circuit and measuring method. The high-precision AD sampling circuit includes an Spullup switch, an Scurrent switch, an Sgain switch, a signal input terminal pair UI-COM, an Rpullup resistor, an Rpoly resistor, an Rcurrent resistor, an Rshunt resistor, an Rseries resistor and a ADC sampler, the signal input terminal UI is connected with the Spullup switch and the Rpullup resistor in turn, the Rpullup resistor is additionally provided with a Vpullup voltage, the signal input terminal UI is electrically connected with the Rpoly resistor, the Rseries resistor and the ADC sampler in turn, the Rpoly resistor is electrically connected with the Scurrent switch, the Rcurrent resistor, and the signal input terminal COM in turn, the Rseries resistor is electrically connected with the Sgain switch, the Rshunt resistor, and the signal input terminal COM in turn, the Rseries resistor is electrically connected with a polarity capacitor and the ground; and the signal input terminal COM is electrically connected with the ADC sampler. According to the invention, the circuit is changed to a variety of configurations by the electronic switches Spullup and Sgain, and the relationship between the variables is listed according to the circuit principle, so that the actual circuit characteristic parameters can be obtained.