The real-time monitoring of hydrogen peroxide (H2O2) is significant for understanding the working mechanism of signal molecules, breeding for stress tolerance, and diagnosing plant health. However, it remains a challenge to realize real-time monitoring of the dynamic H2O2 level in plants. Here, we report an implantable and self-powered sensing system for the continuous monitoring of H2O2 level in plants. A photovoltaic (PV) module is integrated into a sensing system to collect sunlight or artificial light in the planting environment in order to continuously power an implantable microsensor. The transmission process of the H2O2 signal was monitored and analyzed in vivo, and the time and concentration specificity of the H2O2 signal for abiotic stress were resolved. This implantable system provides a promising analysis tool for key signal molecules in plants and might be extended to the real-time monitoring of signaling molecules in other crops.