Marine actinomycetes possess great capacity in producing special metabolites due to their special environment and unique properties in physiological characters and genetic background. In this study, sponge was used as isolation material to explore the resources of symbiotic actinomycetes with antibacterial activity. Firstly, an active actinomycetes strain, ITBB-ZK-a5, was isolated and purified from the sample of Xisha sponge by plate separation method. The strain was identified as Streptomyces by analysis of the phylogenetic tree based on 16S rRNA gene sequence and colony morphological characteristics. Secondly, the inhibitory spectrum of strain ITBB-ZK-a5 against plant pathogenic fungi was studied by plate confrontation method. The results showed that ITBB-ZK-a5 had a broad antibacterial spectrum, in which the 16 tested pathogenic fungi were inhibited significantly. ITBB-ZK-a5 also showed good antibacterial activity in 14 days and 30 days. In order to explore the reason why strain ITBB-ZK-a5 can inhibit the growth of pathogenic bacteria, the antibacterial activity of asepsis agar from the ITBB-ZK-a5 edge were determined, and the results showed that the antibacterial rate were negatively correlated with colony distance. This result revealed that actinomycetes maybe can secrete active substances to inhibit the growth of pathogenic bacteria. Thirdly, the strain had a good antibacterial stability by detecting the antimicrobial activity of five continuously dynasties. Again, light stability and thermal stability of the ITBB-ZK-a5 crude extracts from the rice solid fermentation were tested through the filter method; the results show that with the increase of bath temperature and UV duration, the antibacterial activity of the strain ITBB-ZK-a5 crude extracts were decreased. Finally, the EC₅₀ value of strain ITBB-ZK-a5 against anthrax diseases of banana and papaya were determined. Plant diseases infected by fungi are the main agricultural diseases, and chemical pesticides are the most commonly used method in diseases control. However, the widespread use of chemical pesticides will not only enhance crop resistance to drugs, but also cause pollution to the ecological environment. More importantly, pesticide residues also have a certain influence on human health. Therefore, the common goal of the world is to find more green, efficient and safe control methods. Actinomycetes are found to have biological control effects. The symbiotic actinomycetes isolated from sponges have an inhibitory effect on pathogenic fungi of tropical crops, which can be applied to efficient diseases control, conforming to the concept of green environmental protection. In this paper, we isolated and identified the strain ITBB-ZK-a5, symbiotic actinomycetes from South China Sea sponge, which has the activity of inhibiting pathogenic fungi of various tropical crops, and studied its antibacterial activity, providing a research basis for the development and utilization of biocontrol strains in the future.