【Objective】 To explore the relationship between hidden blood loss （HBL） and risk factors in percutaneous endoscopic interlaminar discectomy （PEID）. 【Methods】 We retrospectively analyzed 113 patients （67 males and 46 females， aged 21-71 years old） with lumbar disc herniation （L5-S1 level） who underwent PEID with complete clinical data in the Department of Spinal Surgery of Subei People’s Hospital Affiliated to Yangzhou University from January 2018 to August 2020. The collected data included general patient indicators （age， body mass index and gender）， underlying diseases （hypertension and diabetes）， laboratory tests （prothrombin time， activated partial thromboplastin time， fibrinogen， hematocrit and hemoglobin level）， imaging related parameters （grade of intervertebral disc degeneration， interlaminar space height and soft tissue thickness of interlaminar approach）， intraoperative significant blood loss and operation time. According to the Gross formula， total blood loss and HBL during operation were calculated. And the risk factors of HBL was analyzed. 【Results】 The total perioperative blood loss was （394.85±130.50） mL， and HBL was （337.09±124.98） mL which accounted for 85.4% of the total blood loss. Multivariate linear regression analysis showed that operation time （P<0.001） and disc degeneration grade （P=0.020） were independent risk factors of HBL. 【Conclusion】 HBL is the main cause of blood loss during PEID， and operation time and disc degeneration grade are independent risk factors that affect the amount of HBL.