Objective  To objectively analyze ocular torsion during inferior oblique overaction （IOOA） with or without V-pattern exotropia and to explore the role of master eye and slave eye and the difference between them. Methods  In this prospective study， based on whether V-pattern strabismus occurred， an experimental group of 51 exotropic patients with IOOA were divided into two groups： 21 cases of IOOA and 30 cases of IOOA with V-pattern. Thirty cases for study of the foveal disc torsional angle （FDA） of the master eye and slave eye without strabismus were selected as the control group. All of the patients in the experimental group underwent inferior oblique weakening and horizontal strabismus surgery and were followed up postoperatively for one month. The FDAs of the master eye and slave eye of the two groups were compared with those of the control group. Data were analyzed using ANOVA and Fisher′s exact test. Results  One month after surgery， the IOOA of the 51 patients with exotropia was no longer apparent， and V-pattern strabismus disappeared in all the patients. There were statistically significant differences in the FDAs of the master eyes between the group with IOOA with V-pattern exotropia and the control group preoperatively （P<0.05）， but no statistically significant differences between the group with IOOA and the control group preoperatively （P>0.05）. There were no statistically significant differences in the FDAs of the master eye between the two groups and the control group postoperatively （F＝0.610， P>0.05）. There were no statistically significant differences in the FDAs of the slave eye between the two groups and the control group before or after the operation （F=1.007， 1.383， P>0.05）. The case of encyclovergence in two groups was increasing. The improvement ratio of near distance stereoscopic is 57% in IOOA group， and 60% in IOOA with V-pattern group. There was no statistically significant difference between two groups （P>0.05）. Conclusion  Excyclovergence in the master eye with IOOA with V-pattern strabismus can be more apparent than in the normal persons. Excyclovergence in the slave eye in IOOA is not as obvious.