This study focuses on the film-forming characteristics of the secondary lubricating medium in water environment under different working conditions, and the roller-on-disc lubrication film test rig along with the fluorescent approach are used to directly observe the film formation of the secondary lubricating medium. Observations reveal that working conditions of higher load and higher speed can decrease the film-forming ability of the secondary lubricating medium but benefit to the stability of the oil film thickness. Block-on-ring test rig and the confocal microscopy are used to prove the characteristics of friction and wear reduction of the injected secondary lubricating medium, and the flow condition of secondary lubricating medium in the contact region of the block-on-ring test rig is then simulated by using the CFD model. This research facilitates the adoption of environmental-friendly lubricants as the secondary lubricating medium in engineering applications lubricated with pure water by providing essential data support.