Thermal stability could significantly affect the processing and sensory properties of milk. Accurately determining the thermal stability of milk is of great significance for optimizing the processing conditions of liquid dairy products. However, the current stability evaluation method on liquid milk is mainly through the observation of stratification, precipitation, or dynamic light scattering technology. There is no fast and reliable and quantitative evaluation standard, which seriously restricts the selection efficiency of the heat treatment process of liquid milk. Turbiscan multiple light technology can test the stability of the fluid without pre-processing the samples. It can monitor the backscattered light and transmitted light intensity of the samples timely, and calculate the migration rate of the internal particles and the thickness of the precipitate layer. In this study, the dynamic light scattering test results were used as control. The Turbiscan multiplex light technique was used to measure the heat stability of skim milk treated with different pre-heating pH values, including pH 6.3, 6.5, 6.7 and 6.9 at 80 ℃ for 30 min. The concentration of CaCl2 before heating was 0, 20, 40, 60 and 80 mmol·L-1, respectively. The results showed that when the CaCl2 increased from 20 to 80 mmol·L-1, the z-average diameter of skim milk changed from 152.7 to 1 284 nm, and the instability index values (after 20 h) increased from 0.98 to 17.04; the backscattered light intensity change value decreased from -4.3 to -37.4, and the backscattered light intensity change value from the bottom end increased from 2.2 to 14.7. When the pH values were 6.3, 6.5, 6.7 and 6.9, respectively, the z-average diameters of skim milk were 148.1, 152.7, 132.4 and 122.4 nm, respectively, and the instability index values 1.20, 1.32, 1.02, 0.98 and 1.41, respectively; the backscattered light intensity values at the top of the sample were -3.1, -4.7, -4.2 and -5.6, the backscattered light intensity changes at the bottom were 5.7, 3.4, 4.1, and 6.8, respectively. The results showed the heat stability of milk can be significantly influenced by the CaCl2, while the pH value has little effect on the thermal stability of skim milk. At the same time, it is also found that compared with dynamic light scattering technology, Turbiscan multiple light scattering technology was more accurately, conveniently and quickly to obtain the stability index, such as milk backscattered light intensity value and instability index. This research has important guiding significance for optimizing dairy processing technology. The Turbiscan multiplex light technology is more convenient and faster than the dynamic light scattering technique.