Abstract Cloud droplet size distribution (DSD) is essential for quantifying the roles of clouds in earth system, including cloud albedo, precipitation formation, and cloud lifetime. The response of cloud droplet spectral relative dispersion (ε) to aerosol number concentration (Na) as well as the role of turbulence in this response are yet puzzling. This study uses large eddy simulation to examine the ε–Na relationship and derives an expression for ε from a minimal model to elucidate this relationship. Our findings indicate that as Na increases, ε initially decreases because aerosols weaken turbulence‐induced broadening more than condensational narrowing. However, as Na continues to rise, ε increases as aerosols weaken condensational narrowing more significantly than turbulence‐induced broadening. These findings improve the understanding of the aerosol effects on cloud DSD and address the challenge of quantifying aerosol indirect effects considering turbulence, potentially leading to new cloud microphysics parameterizations.