Objective: To explore the clinical application value of a preset marking line in lacrimal endoscopic surgery  and evaluate its effect on surgical complications. Methods: This was a prospective analysis of clinical  data from 60 patients (60 eyes) with lacrimal duct obstruction who had lacrimal endoscopic surgery in  Changshu No.2 People's Hospital from June 2015 to December 2018. All patients were divided into two  groups, a control group or observation group according to the even or odd numbers assigned to hospital patients. The control group (odd numbers) had no intra-surgery preset marking line. The observation group  (even numbers) had an intra-surgery preset marking line. The complications of lacrimal duct mucosa injury,  hemorrhage, perforation (false passage), eyelid edema and postoperative hemorrhage were observed and  recorded. The data were analyzed by a Chi-square test. Results: In the observation group, the number  of preset marking lines could be clearly observed during surgery, and combined with the position of the  lacrimal endoscope, could be determined by the anatomical characteristics of the lacrimal passage. One  marker line could be observed in the lacrimal canaliculi. The convergence of two marker lines could  be observed in the common canaliculus. Two marker lines with an enlarged space could be observed in  the lacrimal sac. Two marker lines with mucosal folds could be observed in the nasolacrimal duct. The  incidence of lacrimal mucosal injury was 16% (χ2 =8.543, P=0.003), hemorrhage incidence was 13%  (χ2 =8.718, P=0.003) and eyelid edema incidence was 10% (χ2 =4.069, P=0.044) in the observation group,  which were significantly lower than the incidences in the control group (52%, 52% and 35%, respectively).  One case of perforation (false passage) occurred in the control group, which was not statistically significant  compared with the observation group (χ2 =0.001, P=0.973). There was no statistically significant difference  in the incidence of postoperative hemorrhage between the groups (χ2 =1.898, P=0.168). Moreover, all  patients in the two groups had a small amount of hemorrhage, which did not affect the operation after  intraoperative water injection. Patients with a small amount of postoperative hemorrhage stopped bleeding  within 2 days. Conclusions: The application of preset marking lines for lacrimal endoscopic surgery can  better control the endoscopic examination and surgery, and can accurately identify the location site of the  surgery, which can reduce the incidence of surgical complications.