Dendrobium nobile Lindl polysaccharides (DNLP) exhibited various biological functions. This study aimed to investigate the protective effects of DNLP on testicular spermatogenic function in streptozotocin (STZ)-induced diabetic rats in comparison with metformin. The blood glucose level was significantly increased and the homeostatic model assessment for insulin resistance (HOMA-IR) aggravated markedly in diabetic rats. The weight of testis and epididymis, and the sperm number and motility were decreased in the diabetic rats. The pathologic changes occurred in the spermatogenic tubules along with the decreased number of spermatogenic cells, downregulated proliferating cell nuclear antigen (PCNA) and Sirtuin 1 (SIRT1) expression and increased cell apoptosis in the testes. Compared with the model group, DNLP and metformin treatment significantly decreased the level of blood glucose, improved the HOMA-IR, and increased the weight of testis and epididymis, as well as the sperm number and sperm motility. Furthermore, the pathologic changes in the spermatogenic tubules improved significantly with increased number of spermatogenic cells, the upregulation of PCNA and SIRT1 and suppression of cell apoptosis in the testes. Collectively, our study for the first time examined the effects of DNLP on the male reproductive system of STZ-induced diabetic rats, and indicated that DNLP was protective against diabetes mellitus-induced testis injury via increasing the proliferation, inhibiting cell apoptosis and upregulating SIRT1 expression in testicular spermatogenic cells.