Abstract: The grasp of the oil droplet size distribution is the premise of the research on the behavior and fate of subsurface oil release, and is also the important basis for the effective emergency response during oil spill.In this study, atest facility with the dimensions of 1 m×1 m×2 m (length×width×height) was established for conducting experiments of subsurface oil release of Penglai 19-3 crude oil.The oil droplet size distribution and volume median diameter d₅₀ were chosen as the index to evaluate the influence of nozzle diameter and release velocity on the droplet breakup.The results showed that the ratio of droplets volume was small with the droplets size smaller than 100 μm and larger than 700 μm.Most of the oil droplet size distributions were between 100 μm and 700 μm, and the maximum volume ratio was different under different release conditions.When the nozzle diameter was considered as a constant value, the cumulative volume of smaller droplets increased with the increasing release velocity, and the larger droplets decreased gradually.The d₅₀ decreased as the release velocity increase, and showed a linear correlation with the release velocity after log transformation.The results of this study can provide an important basis for prediction of subsurface oil spill behavior and trajectory.