Abstract: This study investigates how different carbon-containing absorbents affect the transient phase change expansion of liquid oxygen. Specifically, we prepared 3 types of liquid oxygen charges with varying carbon contents (0, 0.1 g, and 0.2 g). A high-speed schlieren system and an overpressure measurement system were used for comparative analysis on the propagation patterns of gas precursor and phase change products in the schlieren flow field and the intensity changes of the phase change gas pressure. Both theoretical and experimental analysis were conducted to unveil the propagation patterns, evolution process and pressure distribution of the phase change gas in the air flow field. Results show that ① Carbon content exerts a significant regulatory effect on phase change expansion. As the carbon content increased from 0 to 0.2 g, the initiation time increased from 1.32 ms to 3.69 ms, and the cumulative pressure time increased by 180 %. ② The propagation speed of the gas precursor exhibited significant increase, with maximum horizontal speed rising from 473.96 m/s to 692.71 m/s and vertical speed from 875.00 m/s to 1 604.17 m/s. ③ Peak overpressure showed nonlinear growth, with axial overpressure increasing from 7.754 MPa to 16.567 MPa and radial overpressure from 1.301 MPa to 4.838 MPa. ④ Separation time between the gas precursor and the phase change products increased from 60 μs to 110 μs. Vertical displacement generally exceeded horizontal displacement, showing an anisotropic propagation pattern of "rapid vertical expansion and slow lateral spread".