The allochthonous input of detritus is the most important sources of energy in headwater streams. The decomposition of allochthonous organic matter as a fundamental ecosystem process for maintaining the balance of carbon and nutrient, is driven by a diverse array of benthic decomposers, but their contribution to the mixed litter decomposition is not well understood. In this study, we addressed the effects of the litter identity and benthic decomposers on the decomposition of litter mixtures in the Jinfo Mountain stream, a typical subtropical headwater stream in southwest China. We collected the three riparian plant species with different lignin to nitrogen ratios (Alangium chinense, Liquidambar acalycina and Machilus leptophylla) and designed seven combinations of the riparian plant species (i.e., three single species including, and four-mixed species). Then the litterbags of three mesh sizes (i.e., 0.05mm, 0.25mm, and 2mm) were chosen in the experiment to identify the effects of microbes, meiofauna and macrofauna. The results showed that:(1) microbes were the main contributor and their relative contribution of microbes in the litter decomposition process was greater than 50%; and both the meiofauna, and macrofauna further accelerated the litter decomposition process. (2) There were significant differences in the decomposition rates among single species:A.chinense (53.05% mass loss rate)>L.acalycina (30.00%)>M.leptophylla (12.63%). The higher quality (higher N and P content and lower C/N and C/P) of leaf litter, the faster decomposition process and the higher the microbial contribution; the lower quality of leaf litter, the slower decomposition process and the higher contribution of invertebrates. (3) For the mixed litter species, there was the significantly negative non-additive effect in the three treatments containing A. chinense (i.e., A. chinense+L. acalycina, A. chinense+M. leptophylla and A. chinense+L. acalycina+M. leptophylla, respectively) in the fine-mesh bags allowing the access of microbes. In the presence of microbes and meioinvertebrates, the non-additive effects of litter decomposition were positive but not significant. Moreover, in the coarse-mesh bags with the presence of microbes, meiofauna and macrofauna, the positive non-additive effects were significant in the two treatments (i.e., L. acalycina+M. leptophylla and A. chinense+ L. acalycina+M. leptophylla, respectively). When the number of mixed litter species increased, the complementation effect between species was enhanced, and the litter decomposition process was faster. In conclusion, the function of litter decomposition in the subtropical headwater streams is closely related to the identity of riparian plants and the complexity of decomposer groups.