The hygroscopicity of aerosol nanoparticles plays an important role in cloud condensation nuclei activity, cloud formation, and, thus, to change the contributions of aerosol particles to climate forcing. The fundamental questions about interaction of water vapor and aerosol are, however, still under debate: are chemical compositions affecting the hygroscopic behavior? Does size-dependent hygroscopicity influence the cloud condensation nuclei activity and cloud formation? Does the mixing state affect the hygroscopic growth? Do the traditionary thermodynamic equilibrium models take composition, size, mixing state into account?? Here, by combing measurement techniques, thermodynamic modelling approaches, we investigate the hygroscopic behavior of aerosol particles across size range from size, chemical composition, mixing state. Firstly, using nano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) and HTDMA-coating device is to investigate the chemical composition, size, mixing state on the deliquescence of (NH₄)₂SO₄ and NaCl particles. The results show that organics including levoglucosan, 4-hydrobenzoic acid, and humic acid decrease the hygroscopic growth factor of ammonium sulfate in the mixed aerosol nanoparticles, and suppress the deliquescence and efflorescence relative humidity of ammonium sulfate in the mixed particle nanoparticles. Interestingly, there is no significant difference in hygroscopicity between well-mixing and core-shell state for nanoparticles consisting of ammonium sulfate and phthalic acid components. However, there is an obvious size dependence of phase transition of NaCl aerosol particles in the size range from 6 to 100 nm. Hygroscopic growth factor of glucose aerosol particles is clearly decreased in the sub-15 nm size range. But no phase transitions occur for glucose aerosol nanoparticles during deliquescence processes. Thus, chemical composition, size, and mixing state should be taken into model account. A differential Köhler analysis (DKA) with size assumption is introduced to cloud parcel to simulate the size effect on the cloud condensation nuclei activity and water condensation. Our findings are essential to understanding atmospheric particles’ effect on climate, air quality, and the ecosystem.