In hydrous ethanol-diesel dual-fuel combustion modes, premixed hydrous ethanol would have an impact on the diesel combustion and soot production. In this work, based on computational fluid dynamics (CFD) model coupled with kinetic mechanism, the influence of premixed hydrous ethanol on combustion and soot formation of n-heptane spray flame in the combustion vessel was investigated, and the influence of different parameters of premixed atmosphere on the n-heptane spray combustion was also explored. The simulation results indicated that the premixed atmosphere could inhibit the n-heptane spray combustion. The ignition delay (ID) time and the flame lift off length (FLoL) gradually increased, and the soot generation decreased with a rise of water content and ethanol premixed equivalence ratio. In addition, compared with the chemical inhibitory effect of oxygenated ethanol molecule on the ID time of n-heptane, the impact of the decrease in charge temperature caused by the hydrous ethanol vaporization on the ID time was more obvious. It could also be found with the reduction in the ambient O2 concentration, the ID time and FLOL of n-heptane increased, and the soot generation significantly reduced. However, if the initial ambient temperature was high as 1000 K, the combustion of hydrous ethanol would enhance the charge temperature, which counteracted some combustion delay effect caused by the premixed atmosphere.