Diesel spray characteristics under hydrogen atmosphere were researched by employing backlighting techniques in a virtual high-pressure constant-volume vessel under an environmental pressure of 2 MPa and an environmental temperature of 293 K. The effects of hydrogen volume fraction λH and fuel injection pressure pinj on the macroscopic and microscopic characteristics of diesel spray were discussed in detail. Furthermore，based on the spray characteristics results，this study clarified the effect of microaddition of hydrogen on diesel combustion characteristics. The results indicate that：the spray penetration increases with λH，but the curves overlap when pinj≥120 MPa. The spray cone angle initially decreases and then slightly increases with λH，but when pinj≥120 MPa，the spray exhibits intense fluctuations，and the angle changes irregularly. Small amounts of hydrogen addition(λH≤9.0%) significantly reduce droplet size，and the sauter mean diameter(SMD) decreases by 1.45% when λH＝9.0% compared to that of no hydrogen addition. Excessive hydrogen addition(λH≥25.0%) inhibits secondary atomization of the spray，resulting in increased droplet size. Due to the vortex effect，droplet size first decreases and then increases radially at lower λH，while at higher concentrations，it increases slowly along the radial direction. Microaddition of hydrogen in the atmosphere alters the diesel ignition delay time. The ignition timing is 3.55 ms after the start of injection(ASOI) when λH＝1.5%，and 2.70 ms when λH＝3.0%. As λH increases，intensity of combustion first decreases and then increases，while the duration of large-area combustion extends，leading to a more uniform distribution of diesel ignition points.