This research aims to explore the efficiency and safety of endoscopic combined intrarenal surgery (Micro-ECIRS) composed of micro-percutaneous nephrolithotomy (Micro-perc) and retrograde intrarenal surgery (RIRS) in the Galdakao-modified supine Valdivia (GMSV) position for a single session for the treatment of complex nephrolithiasis in children. This study retrospectively reviewed patients aged < 18years who underwent Micro-ECIRS in the GMSV position for renal stones larger than 2cm under ultrasound guidance between August 2020 to May 2022 at our institution. A total of 13 patients (8 males and 5 females) received Micro-ECIRS for renal stones under ultrasound guidancewhile adopting the GMSV position. The average stone size was 2.7cm (range: 2.1-3.7cm). Among them, 6 patients had left kidney stones, 5 patients had right kidney stones, and 2 patients had bilateral kidney stones. The mean operative time was 70.5min (range: 54-93min). The mean hospital stay was 6.4days (range: 4-9days). The mean hemoglobin decrease was 8.2g/L (range: 5.1-12.4g/L). The total number of kidneys that had complete stone clearance was 8 kidneys at 48h postoperatively, 11 kidneys at 2weeks postoperatively, and 14 kidneys at 1month postoperatively. Our results demonstrate that Micro-ECIRS while patients are in the GMSV position is a safe and effective method for the treatment of complex children nephrolithiasis. However, all children made three hospital visits and received anesthesia three times. Further research is needed to confirm these findings.