Background: Tissue-specific long non-coding RNAs (lncRNAs) represent potential biomarkers. The testis-enriched lncRNA41584, previously identified as downregulated in male-sterile silkworm mutants (JMS, GMS), is associated with male sterility, but its functional mechanism remained unknown. Subcellular localization, dual-luciferase reporter assays, MTT, and flow cytometry were employed to examine lncRNA41584–miR-3047-z–BmCDK20 interactions. In vivo functional validation included lncRNA41584 knockdown and miR-3047-z overexpression in Bombyx mori. lncRNA41584 localizes predominantly to the cytoplasm and acts as a competing endogenous RNA (ceRNA) by sponging miR-3047-z, thereby upregulating the cyclin-dependent kinase BmCDK20. Perturbation of this axis impaired BmN cell proliferation, causing G1 phase arrest, and led to spermatocyst malformation, reduced fertilization rates, and increased unfertilized eggs. The lncRNA41584–miR-3047-z–BmCDK20 ceRNA network is essential for testicular cell cycle progression and spermatogenesis in silkworms, offering mechanistic insights into lepidopteran male sterility and potential targets for pest fertility regulation.