Streptomyces is a biocontrol agent capable of protecting walnut from stem rot disease caused by the fungal pathogen Cytospora chrysosperma. Antagonistic strains were selected from walnut rhizosphere soil for biocontrol of the disease. The strains were screened using C. chrysosperma as the target pathogen. Using dilution coating plate separation method, plate confrontation method, growth rate method and in vitro branch protection experiment, screening the antagonistic actinobacteria with inhibitory effect and control effect on walnut tree rot disease. Strains were identified based on their morphological, physiological, and biochemical characteristics, 16S rDNA sequencing, and phylogenetic analysis. The strain F-02 was identified as Streptomyces Lavendulae. Plate confrontation method tests showed that the inhibition rates of the Streptomyces strain F-02 on the pathogens were approximately 80.30%. Further study showed that the filtrate of strain F-02 couldinhibit the C.chrysosperma, and the widths of their inhibition zone reached 1.24±0.15 mm, the prevention effect of 71.03%. For the first time, S.lavendulae was used for the biological control of walnut tree rot. It provides strain resources for the development of walnut rot agents. It has potential applications for biological control of walnut tree rot disease.