Abstract: The compost test in the automatic composting device using banana straw, chicken manure and bagasse was conducted to analyse the dominant microorganisms changes under different proportional composition between banana straw and bagasse during the composting process. The results showed that the changes of the microbial total count were wavelike, the same as the changes of the count of bacterium and actinomycete, and the changes of the count of fungi were downtrend. During the whole compost, the count of the mesophilic microorganism was always more than that of the thermophilic, and the count of bacterium was always maximal. accordingly bacterium was the preponderant flora of banana straw compost. The result synchronously showed that it not only could elevate the composting temperature, but also could increase the count of microbial community by adding appropriate proportional bagasse in the treatment of banana straw composting. And the optimal ratio of banana straw to bagasse was three.