Flower-visiting insects have co-evolved with flowering plants. While it has been shown that floral traits and environmental factors influence insect visitation during the day, it is still unclear how these factors influence their visitation at night. We sampled a montane meadow located near Jilin in northeastern China in July and August of 2019, for 4 nights each month, and two time periods each night. We sampled 94 flower-visiting insect species in total and documented floral traits and ambient factors. We first allocated all the insects to three functional groups (pollination, predation, and herbivory). Most nocturnal insects exhibited predation behavior, and had the highest species turnover rate. We then focused on environmental factors and found that ambient temperature and relative humidity strongly influenced the diversity of flower-visiting insects. In addition, variation partitioning analysis suggested that ambient temperature had a stronger effect on the flower-visiting insects during the early night hours, whereas relative humidity had a stronger effect on them in the later night hours. Finally, focusing on floral traits, most insects preferred flowers with moderately sized corolla diameters (20 to 30 mm). Furthermore, display size had a strong linear correlation with flower-visiting insect species richness and frequency of presence. In sum, our findings suggest that ambient temperature, relative humidity and floral display size strongly regulate the behavior of nocturnal flower-visiting insects.