Abstract: Research on CO₂ phase change blasting has historically fallen behind field practice as a powerful alternative to explosive rock-breaking technology. The jet generated by CO₂ phase change blasting serves as the primary force behind the fracturing of rock mass. A comprehensive CO₂ blasting jet test system was developed, utilizing high-speed infrared and standard high-speed cameras, based on the principle of rock splitting in CO₂ fracturing technology and the ultra-high under-expansion jet of CO₂. The research explored the characteristics of blasting jets as they evolved from various types of fracturing devices across different shear thicknesses. The results show that the initial jet of CO₂ blasting represents a typical ultra-high under-expansion jet, characterized by significant instability and varying morphological features at different stages. The shape of the initial blast jet of the Type 95 fracturing device is notably influenced by the expansion wave, transforming from an oval to an approximately spherical shape. The evolution of the jet encompasses intricate phase changes. The CO₂ phase change blasting jet experiences injection initiation, dynamic expansion, and stable development, resulting in a complex flow of a gas-solid two-phase mixture. As the thickness of the shear slice increases, the diffusion length of the visible cloud axis also expands, whereas the boundary gain of the diffusion capacity diminishes. Furthermore, the maximum diffusion velocity along the jet axis increases. In the high-temperature expansion phase, the core temperature of the jet rises dramatically, surpassing the temperature measurement limit by 184.133 ℃, resulting in the jet angle approaching nearly 180°. As the shear slice thickness increases, both the duration of the over-temperature region and the proportion of 'over-temperature pixels' in the CO2 blasting jet rise accordingly. This study offers essential data and experimental backing for additional exploration of the rock-breaking mechanisms associated with CO₂ blasting jets.