Litter is the products of plant metabolism during its growth and development, and is an important way of soil organic matter inputting. Litter decomposition is one of the key processes of ecosystem nutrient cycles. Under the background of global climate change, the frequency and intensity of drought events in tropical areas are both increasing. Meanwhile, it is generally believed that the tropical systems are soil phosphorus (P) limited. Therefore, it is necessary to explore the effects of drought stress and soil P availability on leaf litter decomposition and figure out whether there is an interaction between drought stress and soil P availability in tropical forests, which would be helpful to understand the way that drought stress affects leaf litter decomposition and reveal whether it is regulated by soil P availability or not. Here we conducted a leaf litter decomposition experiment on the floor of a lowland tropical rainforest in Ganzha Ridge, Sanya, Hainan Province. The forest was treated by a two-factor interactive control experiment of throughfall reduction and P addition which was established in 2019. We selected four type of tree species leaf litter, i.e., Hopea exalata, Koilodepas bainanense, Memecylon nigrescens and Acronychia pedunculata, based on dominance, carbon allocation type and leaf texture. The experiment included four treatments, i.e., the simulated drought (D, 50% throughfall reduction), P addition (P, 50Kg P hm^-2a^-1), simulated drought×P addition (DP, 50% throughfall reduction×50Kg P hm^-2a^-1) and control (CK). All treatments were randomly distributed in each one of the three blocks which were made three replicates. By employing litterbag method, we investigated the variations of decomposition constants, litter carbon (C) and nitrogen (N) losses of four-tree species under the four treatments. Our results showed that the four-tree species litter with different litter qualities decomposed differently, and the simulated drought inhibited litter C and N losses of the four-tree species differently, by weakening litter physical fragmentation indirectly and the activities of soil decomposers. Also, the simulated drought decreased four-tree species litter decomposition constants differently, because leaf litter with high quality was much more affected by simulated drought which is more easily decomposed by microorganisms. P addition treatment promoted litter C loss and restrained litter N loss, because increasing soil P availability improved soil microorganisms' ability to decompose high-carbon materials and made microorganisms preferring to take use of the nutrient to grow and metabolize rather than use them to produce enzyme related to decomposing litter. There was a significant interaction between the simulated drought and P addition on decomposition that P addition alleviated or reversed the inhibition of simulated drought on litter decomposition. The results suggest that four-tree species leaf litter with different qualities decompose and response to simulated drought differently; P addition would accelerate litter C loss and inhibit litter N loss; Soil P availability could regulate the effects of simulated drought on leaf litter decomposition in lowland tropical rainforest.