Based on the principle of dynamic light scattering, this paper develops a set of dynamic light scattering apparatus which can measure the thermal diffusivity. The experimental system includes scattering light path, pressure vessel, temperature control system, and data acquisition system. The optical fiber is introduced into the dynamic light scattering system as a probe, which reduces the experimental system to 1/3 of the similar system. In this paper, the reference fluid n-hexane was used to test the accuracy of the experimental system. The thermal diffusivity obtained from the experiment was fitted into a polynomial equation with a maximum deviation of 0.19%, an average absolute deviation of 0.11%, and the maximum deviation between experimental and literature values was 3%. After uncertainty analysis, the uncertainty of liquid thermal diffusivity measured by the newly developed dynamic light scattering experimental system is 2% (k=2).