The artificial rainfall method was used to create the simulated hydrograph, and soil column experiments were performed to examine the effect of bioretention on thermal pollution control of runoff, with different rainfall durations, different service areas, and different depths of internal water storage. The results showed that bioretention had a great thermal pollution control capacity under the experimental conditions, and soil temperature at a depth between 92.5 cm and 115.0 cm was the lowest and most stable. The reduction rate of rainfall thermal pollution firstly increased and then decreased with the extension of rainfall duration for the same service area, and the optimal thermal pollution reduction rate changed with bioretention design parameters accordingly. The ratio of bioretention area to its service area is an important factor, and the reduction rate of thermal pollution increased from 23.19% to 38.02% when the ratio increased from 1∶20 to 1∶5, with a decreasing fluctuation range of the effluent temperature. In addition, internal water storage structure can improve the effect of bioretention on thermal pollution control by intercepting runoff and promoting its infiltration to replenish groundwater.