In this study, the effect of medium saline water on the synergistic interaction between diesel and Triton X-100 in the flotation of oxidized coal was investigated. The results showed that the flotation yield of oxidized coal in saline water was higher than that in de-ionized (DI) water due to the promotion of diesel adsorption, which was attributed to the screening of electrostatic repulsion between diesel droplets and coal particles in saline water. Meanwhile, the flotation of oxidized coal could be significantly improved when Triton X-100 was added with diesel as a composite collector, and less Triton X-100 was required in saline water than that in DI water to achieve the same true flotation yield, indicating that saline water could increase the effectiveness of Triton X-100 in improving oxidized coal flotation. A mechanism study revealed that Triton X-100 was able to promote diesel adsorption on oxidized coal through emulsification, thus increasing the surface hydrophobicity of oxidized coal through hydrogen bonding between the headgroups of Triton X-100 and the oxygenated groups on coal surfaces. The non-ionic characteristic of Triton X-100 ensured its capability of enhancing oxidized coal flotation in both DI water and saline water.