To quantify the volume of hidden blood loss (HBL) between conventional laparoscopic surgery (CLS) and laparoendoscopic single-site surgery (LESS) for ovarian cyst and to explore its risk factors. A total of 310 patients who underwent CLS or LESS were enrolled in this study. The Nadler formula and Gross formula were used to calculate each patient's estimated blood volume and total blood loss, multiple linear regression analysis was applied to identify the risk factors. The HBL in LESS was more than in CLS (P=0.000). Operative time (p=0.015), pre-hematocrit (P=0.002), pre-hemoglobin (P=0.015), and pelvic adhesions (P=0.037) were positively correlated with HBL in CLS. Intraoperative bleeding (P=0.026), operative time (P=0.000), pre-hematocrit (P=0.042), CA125 (P=0.047), and cyst volume (P=0.012) were independent risk factors for HBL in LESS. A large amount of HBL occurs in ovarian cystectomy surgery and cannot be ignored in clinical work; fully and correctly understanding HBL and exploring its causes can ensure the safety and improve the prognosis of patients.