The invention discloses a low-voltage detection system and method in the technical field of power monitoring. The system comprises a central processing unit, and a relay output circuit, a clock circuit, a watchdog circuit, a liquid crystal display and key input circuit, a switching quantity acquisition circuit, a voltage processing circuit, a current processing circuit, an RS485 serial port processing circuit and a power circuit which are connected with the central processing unit respectively. According to the device, an R485 serial port is adopted for networking communication, an MODBUS communication protocol is supported, and the device is a liquid crystal display multifunctional instrument for a real-time power monitoring system, which has the function of measuring power parameters such as harmonic voltage, harmonic current, current and voltage angle, voltage and current value, active power, reactive power and electrical degree at high accuracy. The low-voltage detection system has the advantages of small size, simple structure, modularized design, large liquid crystal display and the like.