To achieve the accurate extraction and characteristics analysis of electrical signal in plants, the system was developed for detecting and extracting weak electrical signal in plants. As experimental platform for the extraction and detection of plants electric signal, training experiment system on the growth of plants, had done the experiments of extraction and feature analysis on plants electric signal by it, described in detail the extraction and analysis process of plants electrical signal, and also discussed the methods of anti-interference process for the system. The system construction is feasible, it has positive significance for real-time monitoring the environment factors changes and the plants growth status.