Understory vegetation plays a crucial role in sustaining biodiversity and ecosystem functions, as well as contributing to forest biomass. It is inevitably affected by land use types and seasonal variations in the tropics. This study investigated the understory vegetation of five typical land use types, namely conventional management of rubber plantation (CR), natural restoration of rubber plantation (NR), artificial restoration of rubber plantation (AR), banana plantation (BP) and secondary forest (SF), in Xishuangbanna, southwestern China. The study aimed to examine the response of species composition, diversity and biomass allocation of understory vegetation to different land use types and seasons. The results showed that: 1) A total of 50 shrub species belonging to 41 genera and 31 families and 88 grass species belonging to 79 genera and 45 families, with perennial herb accounting for more than 60% of the total grass species, were found under five land use types. The dominant group of shrubs were mainly leguminous, and the majority of grasses were of the Poaceae and Asteraceae families. 2) CR and BP, where anthropogenic disturbances were stronger, significantly altered the species composition of understory vegetation and the distribution of dominant groups, as well as decreased the average height, coverage, total biomass, aboveground and belowground biomass of understory vegetation compared to SF, NR and AR, where disturbances were rather weak. Meanwhile, belowground/aboveground biomass ratio of shrub under CR was obviously higher than that of SF, NR and AR, while there was no difference in belowground/aboveground biomass ratio of grass across different land use types. 3) The community structure, diversity and biomass of grass exhibited greater susceptibility to seasonal variability than shrub. The average coverage and height of grass under CR were significantly higher in rainy season than in dry season, while the Pielou index of perennial herb and annual herb diversity under SF were significantly lower in rainy season than in dry season. In addition, the biomass of understory vegetation and its herbaceous layer in all rubber stands were obviously higher in rainy season than in dry season, whereas BP showed the opposite trend. There was no significant seasonal variation in belowground/aboveground biomass ratio for shrub and grass, with the rainy season resulting in an increase in belowground/aboveground biomass ratio for grass plants, due in part to a greater contribution from perennial herb. In conclusion, changes in tropical land use and season had distinct effects on understory vegetation diversity and biomass allocation. This study will provide a scientific basis for biodiversity conservation and sustainable management of artificial economic plantations in tropical region.