Abstract: The observation and study of clouds are of great importance for the development of numerical models, climate change estimation, weather modification, etc. To advance the understanding of structural characteristics and temporal variations of clouds in the mountainous areas along the southeast coast of China, observations from a ground-based Ka-band millimeter-wave cloud radar deployed in Jian"ou of northern Fujian, China, between 2019 and 2022, were utilized to study the characteristics, seasonal patterns, and diurnal variations of cloud occurrences, vertical structures, and parameters in this area. Additionally, the causes underlying these observed characteristics and variations are also discussed from atmospheric water vapor and thermodynamic conditions. The findings indicate that: (1) Cloud occurrence exhibits seasonal variations, with the highest occurrence observed during spring, followed by summer and winter, and the lowest during autumn. Low and high clouds dominate during spring and summer, whereas low and mid-level clouds are predominant during autumn and winter. (2) Radar reflectivity factors of high clouds are generally larger than those of low clouds during spring and summer. In summer, both ice-phase and liquid-phase cloud layers exhibit the largest radar reflectivity factors, followed by spring and autumn, and the smallest reflectivity factors are observed during winter. Cloud base height and top height are highest during summer, followed by spring and autumn, respectively, while they are lowest during winter. The thickest cloud layer and largest cloud gap distance also occur during summer, followed by spring and autumn, respectively, whereas the thinnest cloud layer and smallest cloud gap distance are observed during winter. (3) Diurnal variations in cloud vertical structures and parameters are significant in different seasons, and their differences are also apparent. Compared to spring, summer exhibits earlier and stronger convection activities and a longer lifespan, resulting in larger and longer-lasting variations in cloud parameters during the afternoon. Diurnal variations in cloud occurrence, intensity, and other cloud parameters are less pronounced during autumn and winter compared to spring and summer. However, the diurnal variation trend of clouds in autumn is similar to that in summer, while the diurnal variation trend of clouds in winter is similar to that in spring. (4) Average specific humidity, horizontal wind field, and convective available potential energy show significant positive correlations with the seasonal and diurnal variations in cloud radar-observed cloud-related changes in the local area.