The photovoltaic (PV) array wireless sensor node and fault diagnosis system based on STM32 is designed aiming at the problems of the existing methods of PV array fault detection are lack of accurate and efficient and difficult to locate faulty PV modules. STM32F103 is used as the core controller of the wireless sensor node hardware. It is mainly composed of power module, main control module, data sampling module, data communication module. Using defined communication protocol, the measurement results are reliably transmitted as data frames through ZigBee wireless module, the monitor computer can monitor the voltage data of PV modules in the process of inverter scanning the current-voltage (I-V) characteristics of PV array. In the experiments, the common shading and short-circuit of bypass diode failure of PV modules are artificially caused. The voltage waveforms of PV modules are measured by the wireless sensor node, which can realize fault diagnosis and location in PV array. The experimental results show that the system can obtain the voltage waveform of PV array when the inverter scans the I-V characteristics of PV array, facilitating maintainers to locate PV module faults timely and accurately.