This paper presents a high-precision weighing system based on an AC-excited strain bridge using an STM32 microcontroller. The system employs AC excitation and phase-locked amplification technology, combined with hardware filtering and temperature compensation. By implementing digital phase-sensitive detection algorithms via the STM32, it effectively suppresses temperature drift and interference. Within the 0-5 kg measurement range, the system exhibits nonlinear error below 0.05% FS and a temperature drift coefficient under ±0.001%/°C. It demonstrates excellent dynamic accuracy and environmental adaptability, making it suitable for industrial automation and precision weighing applications.