Abstract：This paper introduces a method for voltage acquisition module device of PLC, and the specific application case in PLC project. The main function of PLC's multi-channel voltage acquisition module is AD conversion of multi-channel analog signals. Through the 485 signal converter, the converted data can be stored in the memory, and the data in the memory can be read out through FPGA. The acquisition precision of the AD is 16 bits and the acquisition range (0-5) V. It is especially suitable for high precision measuring and detecting unit. It is characterized by two main features: one is high precision and two is fast.