Postoperative gastroparesis occurs after surgeries which affect the upper digestive tract. Gastric peroral endoscopic myotomy (G-POEM) is a treatment for postoperative gastroparesis. The present study boasts the long-term efficacy and safety of G-POEM in a large cohort of patients. Gastroparesis Cardinal Symptom Index (GCSI) and Gastroesophageal Reflux Disease Questionnaire (GERDQ) were utilized for the assessment of postsurgical gastroparesis symptoms. Gastroscope was used to observe the anastomotic site. Three-dimensional ultrasound was used to measure the morphological structure of the gastric antrum and pylorus tube. Gastric emptying time was calculated by analyzing the volume change of gastric antrum. Significant clinical effectiveness of G-POEM was observed. The GCSI score, including each subscale score, showed significant decrease after G-POEM. Before G-POEM, there was a negative correlation between GCSI score and the inner diameter of pylorus, as well as a positive correlation with the length of pyloric tube. The similar results were found in the scores of nausea/vomiting and postprandial fullness/early satiety subscales. No correlation was observed between GCSI score and the emptying time, nor between the emptying time and the parameters of antrum morphology. After G-POEM, no correlation was found between GCSI (including subscales) score, the emptying time, and the parameters of antrum morphology. Patients who exhibited as clinical non-responders often accompanied with GERD symptoms. After G-POEM, the score of GERDQ decreased significantly. Either before or after G-POEM, no correlation was noticed between GERDQ scores, the emptying time and the parameters of antrum morphology. The technique of G-POEM was demonstrated as a minimally invasive approach with the long-term efficacy and safety in therapying postoperative gastroparesis.