Abstract: In recent years, the impact of atmospheric bioaerosol particle hygroscopicity on climate and human health has attracted widespread attention, and pollen is an important component of bioaerosols. In order to understand the changing trend of hygroscopicity of pollen particles, five types of pollen particles were collected in Hangzhou, including Camellia, Orychophragmus violaceus, Aquilegia, Weigela florida, Viola tricolor. Scanning electron microscope was used to observe the morphology and structural characteristics of individual pollen particles. An individual particle hygroscopic system was used to observe the hygroscopic growth of pollen particles under different relative humidity (RH). Here we obtained the size distribution of individual pollen particles and their hygroscopic growth factors (GFs). The results show that hygroscopic GFs of Camellia, Orychophragmus violaceus, Aquilegia, Weigela florida, Viola tricolor pollen particles were 1.09, 1.09, 1.08, 1.13 and 1.14 at 90%RH and the hygroscopic GFs were 1.11, 1.10, 1.11, 1.14 and 1.16 at 95%RH, which is lower than the GFs of inorganic aerosols in the ambient atmosphere. We found that the surface of pollen particles had weak size growth through water uptake. In addition, we also noticed that the overall structure and shape of some pollen particles changed during particle hygroscopic growth. For example, scanning electron microscopy images showed that the weigela florida pollen particles in the dry state displayed internal hollow collapse, but the pollen particles transformed from collapsed particles to the spherical shape with increasing RH. These results suggest that pollen particles have weak hygroscopic properties in the atmosphere, and the absorption of water can alter their morphological structures, which is of great scientific significance for understanding pollen hygroscopicity in the human respiratory and cloud condensation nucleation activities in the atmosphere. Studies have shown that pollen types, the number of pollen germination pores and the surface structure of pollen affect the hygroscopicity of pollen, and the hygroscopicity of pollen increases slowly under low humidity and rapidly under high humidity.