Abstract:The effects of different light treatments and GA3 on hook opening, twining and parasitism of Cuscuta australis were studied using LED as light sources for the first time. The results showed that light was a necessary factor for dodders to parasitize the hosts successfully and chemical signals might facilitate host recognition and twining. GA3 involved in controlling twining response，but no distinct effect on hook opening. Furthermore, besides typical phytochrome reaction, another photoreaction called HER was involved in these processes, which could be caused by 879 nm far red light. So it demonstrated directly that there was not only HER in dodders, but also dark conversion from Pfr to Pr, and there were mutual interaction of phytochromes and cryptochromes in twining.