AIM: To evaluate the clinical significance of checking episcleral venous fluid wave (EVFW) during gonioscopy-assisted transluminal trabeculotomy (GATT) in patients with open angle glaucoma (OAG). METHODS: This retrospective case series study comprised 30 patients (45 eyes) with OAG underwent GATT. The location and extent of EVFW were examined and graded after intraoperative compression flushing of the anterior chamber angle during the operation. Patients were followed up for 1y. A complete success for surgery is defined as a postoperative intraocular pressure (IOP) <18 mm Hg without any anti-glaucoma medication. IOP<18 mm Hg with less than two anti-glaucoma medications is defined as qualified success, while the control of IOP requiring three anti-glaucoma medications is considered as unsuccess. RESULTS: The mean IOP was 35.38±7.16 mm Hg before surgery and 15.52±4.22 mm Hg 1y after surgery (P<0.01). The average number of anti-glaucoma medication was 2.8±1.2 (2-4) preoperation and 0.6±1.3 (0-3) 1y postoperation (P<0.01). The success rate of the operation was 93.33%. Complete success rate was 66.67%, qualified success rate was 26.67%, and 6.66% of unsuccessful cases required reoperation. EVFW of all cases was grade 2-4, and the percentages of grade 2, 3 and 4 were 33.33%, 40.0% and 26.67%, respectively. The distribution and percentage of EVFW were inferior (36%), nasal (28%), superior (20%), and temporal (16%). The EVFW grade of complete success patients was 3.4±0.6 (3-4), and that of qualified success patients was 2.6±1.0 (2-4). The larger the range of EVFW, the lower the IOP, and the better the IOP reduction effect. CONCLUSION: During GATT surgery, pressurized irrigation of anterior chamber to check EVFW can reduce the outflow resistance of aqueous humor and increase the effect of postoperative IOP. The range of EVFW is negatively correlated with postoperative IOP. Therefore, EVFW may be a valuable prognostic indicator for the success of GATT surgery.