The invention discloses an analog quantity input module of a DCS. The analog quantity input module comprises a power supply circuit, a CPU module, a communication circuit and a channel acquisition circuit, wherein the power supply circuit is used for supplying power to whole AI module, the channel acquisition circuit is used for transmitting onsite signals to the CPU module, the CPU module is used for communicating with a control station with the DCS through the communication circuit, the channel acquisition circuit is provided with a common-mode inhibition circuit with high input impedance and a common-code inhibition capability, and the common-mode inhibition circuit is used for performing differential mode amplification on the onsite signals and realizing common-mode inhibition at the same time. According to the invention, through the common-mode inhibition circuit with common-mode inhibition, amplification can be performed on a differential mode, a common mode is inhibited accordingly, and the problem of poor anti-common-code interference capability in an AI module in a conventional DCS is solved.