Background To compare the efficacy and safety of ab externo circumferential trabeculotomy (ECT) and canaloplasty on primary open angle glaucoma (POAG) patients with failed filtering surgery and intact schlemm's canal (SC). Methods We conducted a retrospective chart review of POAG patients with failed filtering surgery and intact SC, who further received ECT and canaloplasty. The primary outcome measures were intraocular pressure (IOP) and the number of topical medications at each follow-up point. The secondary outcome compared the quantified success rate at1-year follow-up between the groups. Results Twenty-nine eyes were recruited in the ECT group and 19 eyes in canaloplasty group. The postoperative IOP and the number of topical medications decreased significantly in both groups (p < 0.001). The IOP at 3-month and 6-monthwas significantly lower in the ECT group (p = 0.039,p = 0.001) than in the canaloplasty group. Although the IOP at 12-mon was similar between the two groups, the number of topical medications was less in the ECT group (p = 0.040). Hyphema (72.4%) and ciliary body detachment (27.6%), which mainly resolve spontaneously, were two leading complications in the ECT group. The prevalence of hyphema was higher in ECT than in canaloplasty group (p < 0.001). Conclusion For POAG with failed filtering surgery and intact SC, canaloplasty may be safer, whereas ECT presented better IOP control. Translational Relevance: Suggestions for surgical choice for POAG with failed filtering surgery.