Solubility is one of the important parameters to reflect the reagent solubleness. Some traditional methods such as balance method and dynamic method can measure dissolved balanced end of the reagent,but the human eye visual defects make the experiment results have bigger error and these methods have low efficiency,low degree of automation. Aiming at these problems,an automatic dynamic detection system based on the Lambert-beer law was proposed. The system includes a stable laser source,a sensitive PIN photodiode and a computer dynamic sampling system of temperature-time and light intensity-time. A solid-liquid solubility dynamic testing experiment device was built based on the laser intensity dynamic absorbance. The experimental device was used in a reliability test by using potassium chloride-water system in the range of 10~50 ℃ as a standard system.Results show that the output of the semiconductor laser power is stable and the light intensity range is ±0.7 mW;the solubility error of potassium chloride in water is ±0.005 and this is consistent with that of the literature. The system can overcome the shortcomings of traditional methods and greatly improve the accuracy and efficiency of solubility test and can meet the needs of different industries.