In this study, particle number size distribution (PNSD) and concentration of cloud condensation nuclei (N_CCN) were observed at the summit of Mt. Hua during Dec. 16^th 2020 - Jan. 23^rd 2021. The concentration of nucleation mode particles with the growth ratio of 0.83 nm·h⁻¹ erupted frequently from 13:00 to 18:00 local time due to the intense photochemistry. The explosive increase of the small diameter particles could not be activated into droplets, but they had the potential to adsorb or absorb the polluted gaseous to promote the growth conversion into CCN. In the growth process, relative humidity had reverse effect on diameter and concentration with temperature, while higher wind speed was beneficial for the removal of large particles. SO₂ and NH₃ had a synergistic effect in contributing to the increase of particle diameter and concentration for the relative larger diameter, but NH₃ had inverse effect on the number concentration for the nucleation mode particles. Additionally, the influence of O₃ on the distribution characteristics of particle may be regulated by temperature. The small k value that fitted by two-parameter power model suggested the larger or hygroscopic particles, while larger value for the ultrafine or hydrophobic particles. Hygroscopicity parameters (κ) showed a downward trend with the increase of supersaturation as the source direction of the air mass gradually shifted from northwest to southwest. By comparing the calculated and the measured N_CCN, we inferred that the hygroscopicity parameter decreased from 0.22 to 0.13 with the supersaturation from 0.2 to 1.0% in Alpine region.