Objective To evaluate high resolution esophageal manometry (HREM) in peroral endoscopic myotomy (POEM) for pediatric achalasia of cardia (AC). Methods Data of 30 AC children who received POEM in Xi'an Children's Hospital from January 2013 to September 2019 were reviewed. HREM was performed before and 6 months after POEM. Preoperative and postoperative lower esophageal sphincter pressure （LESP）, 4-second integrated relaxation pressure (4sIRP), Eckardt scores and nutritional status were compared. Results Children with AC aged between 4-14 years. Postoperative LESP was 5.50±1.13 mmHg （1 mmHg=0.133 kPa）, which was significantly lower than that before operation (26.23±4.47 mmHg) with significant difference (t=-24.623, P<0.001). Postoperative median 4sIRP was 5 mmHg, which was 20 mmHg lower than that before operation (25 mmHg) with significant difference （Z=-4.786， P<0.001）. Postoperative median Eckardt symptom score decreased significantly compared with that before (1 VS 8, Z=-4.796, P<0.001). Severe malnutrition of the AC children improved evidently to normal(Z=-5.166, P<0.001). Conclusion POEM can significantly improve the characteristics of esophageal dynamics in children with AC, and HREM can be an important indicator for follow-up evaluation of POEM.