At present, there have been many research results in liquid concentration detection, but China is still relatively backward in optical detection technology, and it is of great significance to research and develop new liquid detection systems. Under the same solute, due to the different concentration of the liquid, its absorption degree of fixed incident light will also be different, the use of photoelectric sensor to detect the change of light intensity, you can obtain the absorbance of the liquid, and then calculate the liquid concentration. Based on the above theory, this paper designs a liquid concentration measurement system based on the main control module of STM32F103RCT6 chip based on ARM Cortex-M3 core. The system consists of an STM32F103RCT6 chip, a TSL2591 photoelectric sensor, a laser emitter, and an OLED display. When the liquid concentration in the container changes, it will cause the light intensity change detected by TSL2591, and according to the change of the obtained data, the data will be fitted with the change of the configured liquid concentration, and finally a curve corresponding to the liquid concentration and the data change is obtained. The value measured by the TSL2591 is substituted into the curve to obtain the concentration value of the liquid and displayed on the OLED display. Through tests, it has been proved that the device can determine the concentration of liquids more accurately. The system has the advantages of simple structure, high sensitivity and fast response time, and can accurately measure the concentration of liquid.