Abstract: The vaporization of ultra-low-temperature liquid oxygen (LO₂) film in mechanical seals of rocket turbopump is much significant under high-speed conditions, decreasing the stability and safety of seals and rockets. Thus, improving the anti-vaporization characteristic is extremely critical. To investigate the anti-vaporization characteristic of face composite channel, a three-dimensional continuous boiling model was developed with considering the complex grooves, viscous shear thermal effect, turbulence effect, viscosity-temperature relationship and coupled heat transfer characteristic of rotor/stator in LO₂ mechanical seals. The fluid pressure, temperature, and phase state distributions were obtained. The anti-vaporization characteristic of composite face channel was evaluated, and the influences of rotational speed, inlet temperature, film thickness, groove depth, and dam ratio on the anti-vaporization characteristic and sealing performance were analyzed by comparing with classical spiral-grooved mechanical seals. The results showed that a significant thermal mixing effect was generated in the composite face channel due to the interaction between the low-temperature LO₂ at outer-dimeter-side and high-temperature LO₂ at inner-dimeter-side. This significantly decreased the temperature of fluid film and sealing end faces, enhanced the hydrodynamic effect, and inhibited the fluid vaporization. Under the viscous friction heat and thermal mixing effect, the fluid vaporization intensified with the increase of rotating speed, LO₂ inlet temperature and the decrease of film thickness. The spiral groove depth and groove-to-dam ratio hardly affected the anti-vaporization characteristic. The vaporization area of seals with the composite face channel was always smaller than the classical spiral-grooved seals under the same conditions. At 25 000 r/min, the vaporization area ratio was 10% and 48% respectively, and it dropped 38%. Meanwhile, the load-carrying capacity was enhanced by 3 388.4 N and the leakage rate was increased by 0.015 9 kg/s.