Abstract: Siemens S7- 200 PLC and visual Basic net are adopted to develop the multi-channel real-time monitor system for the purpose of solving the probelm about the low quality of acid bath procedure reglulation of pectic fibre, big fluctuation of acid density and unability to detect and analyze the variation of acid bath in time. The system adopts SQL server database to storage the original data so as to make it easy to do on-line inquiry and analysis; The real-time monitor system of acid bath has a flexible configuration, extensibility and high reliability. The upper monitoring software can be easily applied, can visually represent the real-time data and original data, and has a flexible function of quiery analysis and printing.