CO2 transportation safety is important for the successful implementation of carbon capture and storage (CCS) projects. The formation of solid CO2 is a unique phenomenon in high-pressure CO2 release. The evolution and size distribution of dry ice particles have a significant impact on assessment of the consequences of accidental release of supercritical CO2 from a pipeline. The motivation is to investigate the particle behavior and size distribution and understand how the impact factors affect them. An experiment with various measurement methods was developed to carry out controllable CO2 release from a high-pressure vessel. The macroparameters such as jet configuration, temperature, and velocity were recorded. Meanwhile, motion of the microparticles was also analyzed. In addition, the effects of initial pressure and temperature on the particle size distribution were investigated. The results showed that the agglomeration influenced the size distribution at different positions of the jet.