Dielectric barrier discharge technology can generate cold plasma at atmospheric pressure, which contains abundant active particles and shows great potential for fresh produce sterilization applications. However, water droplets frequently adhere to the surfaces of fruits and vegetables, which changes key parameters including the gas gap width, dielectric distribution, and gas-phase composition, consequently affecting the effectiveness of plasma applications. Currently, plasma-droplet interactions with contact angle as a variable remain unexplored, and the underlying mechanisms by which adhering droplets affect the electrochemical characteristics of dielectric barrier discharge require further investigation. In this work, we develop an atmospheric-pressure helium dielectric barrier discharge simulation model with an He-O₂-N₂-H₂O reaction system. This model is used to study how water droplets (with contact angles of 45°, 90°, and 135°) adhering to the surface of the specimens affect both the steady-state discharge structure and active particle distribution, as well as their underlying mechanisms. The results show that the steady-state discharge intensity is significantly weakened both at the droplet surface and in the region above it, with the greatest reduction occurring at a contact angle of 135°. During the main positive breakdown phase, the polarized electric field at the droplet surface significantly enhances both electron impact ionization and secondary electron emission, thereby promoting gas-phase breakdown in the region above the water droplet. During the main negative breakdown phase, this polarized electric field accelerates electron migration toward the liquid surface, which intensifies plasma ambipolar diffusion and consequently leads to the formation of an annular discharge suppression zone around the water droplet. During the secondary positive discharge phase, even though the water droplet becomes polarized and a radially inward electric field is generated near the liquid surface, the resulting seed electron scavenging effect suppresses discharge in the region above the water droplet. Due to the stronger polarized electric fields generated at the surfaces of water droplets with larger contact angles, both the discharge enhancement and suppression effects become more pronounced with the increase of contact angle. Regarding the chemical species distribution, active particles and electrons exhibit a synergistic distribution relationship. On the surface of the specimens, He⁺ ions undergo electric field-driven migration, resulting in a highly non-uniform spatial distribution. The evaporation of water droplets provides more reactant sources for OH generation, thereby increasing its total deposition quantity. Because the bond energy of O₂ is lower than that of N₂, oxygen (O) demonstrates a more uniform distribution and a greater total deposition quantity than nitrogen (N). On the surfaces of water droplets, the active particles exhibit a gradually decreasing distribution from the center to the edge. Notably, the total deposition quantity of He⁺ continuously increases with larger contact angles increasing due to the aggregation effect of the polarized electric field. This study systematically elucidates the influence mechanisms of adhering water droplets on the electrochemical processes in dielectric barrier discharge, providing theoretical guidance for relevant applications of plasma-droplet systems.