Abstract: The didynamous of Torenia fournieri showed retroflexion during filament growth. To investigate the physiological mechanism of didynamous retroflexion of T. fournieri, we analyzed the effects of GA3 and NAA, as well as their inhibitors on didynamous retroflexion. The results showed that application of GA3 and NAA shortened the time of retroflexion to 49.1% and 53.6% of that of the control. Furthermore, application of inhibitors of GA biosynthesis and NAA transport, PAC and TIBA, delayed the time of retroflexion to 165.3% and 59.6% of that of the control, which indicate that plant hormones, GA3 and NAA are involved in regulation of didynamous retroflexion of T. fournieri.