Background Spinal cord injury (SCI) due to lack of restoration of damaged axons is associated with sensorimotor impairment. This study was focused on using the human Placental mesenchymal stem cells- exosome (hPMSCs- exosomes) in an animal model of severe SCI under a new myelogram protocol to confirm lumbar puncture (LP) injection accuracy and evaluate intrathecal space. Methods Mesenchymal stem cells (MSC) were extracted from human placenta tissue and were characterized. HPMSCs- exosomes were isolated by ultracentrifuge. After creating the severe SCI model, LP injection of exosomes was performed in the acute phase. Myelogram was also employed. The improved functional recovery of the animals in the treatment and control groups was followed by recording movement scores for 6 weeks. Hematoxylin-Eosin (H&E) staining was used to evaluate to detect pathological changes and glial scar size. The Immunohistochemistry (IHC) of GFAP and NF200 factors as well as the apoptosis tunnel test was investigated in the tissue samples from the injury site Results The results demonstrated that the use of the myelogram can be a feasible, appropriate and cost-effective method to confirm the accuracy of therapeutic agents LP injection and examine the subarachnoid space in the model of laboratory animals. Furthermore, intrathecal injection of hPMSCs-exosomes in the acute phase of SCI can improve motor function by attenuating apoptosis of neurons at the site of injury, decreased GFAP expression and increased NF200 in the treatment group, reducing glial scarring, and increasing axonal regeneration. Improving functional recovery by not creating bedsores in the treatment group and preventing hematuria were other effects of the exosome Conclusions In conclusion, the effects of hPMSCs-exosome can be considered to be not only in restoring function but also in preventing complications and managing symptoms. Thus, the neuroregenerative and anti-apoptotic potential of hPMSCs-exosome can be considered a therapeutic approach in SCI reconstructive medicine.