Sigma-1 receptor (Sig-1R) agonists has therapeutic effects in neurological disorders and possesses properties that can reverse cognitive dysfunction. This study investigated the therapeutic efficacy of Sig-1R activation on cognitive dysfunction in streptozotocin (STZ) combined with high fat and high sugar diet (HFD)-induced type 2 diabetic rats. By employing morris water maze (MWM) testing and computed tomography (CT) imaging, we observed that activation of Sig-1R effectively mitigated brain atrophy and cognitive impairment in diabetes-induced cognitive impairment (DCI) rats. Given the fundamental role of intact hippocampal synaptic plasticity in maintaining cognitive function, we investigated the correlation between Sig-1R and Brain-Derived Neurotrophic Factor (BDNF), a well-established neurotrophic factor. And we also analyzed the expression of Postsynaptic density protein-95 (PSD95) protein. Golgi staining, Haematoxylin-eosin (HE) staining, Nissl staining, and immunofluorescence results show that activating Sig-1R can upregulate BDNF expression and reducing synaptic damage in hippocampal neurons. To elucidate the mechanism by which Sig-1R activation leads to increased BDNF levels, we investigated the Extracellular Signal-Regulated Kinase/Cyclic AMP Response Element-Binding Protein(ERK/CREB) protein pathway. In vitro and in vivo, we observed that Sig-1R activates the ERK/CREB signaling pathway, thereby stimulating BDNF release and increased PSD95 expression. Further intervention with BD1047 antagonist and Tropomyosin-Related Kinase B (TrkB) antagonist ANA-12 confirmed our conclusion that Sig-1R activation upregulated p-ERK and p-CREB protein expression, promoted BDNF transcription, the expression of PSD95 protein was up-regulated, reduces synaptic damage in damaged hippocampal neurons, and rescued cognitive impairment in DCI rats.