Aiming at the detection of water pollution, an online real-time detection system of water turbidity based on STM32 is designed. Based on the transmission method in ISO7027—1984, the system determines the turbidity of water samples by measuring the attenuation of the transmitted light intensity by striking a beam of light into a water sample with a certain thickness. The experimental results show that the average relative error between the actual measured value and turbidity standard liquid value is less than 4%. It is feasible to realize the real-time monitoring of water turbidity. The designed system has the advantages of low cost, small volume, convenient carrying, and simple detection mode, and can be used for water quality monitoring in daily life.