A thermal siphon structure includes a main body, a chamber disposed therein, an evaporation section, a condensation section and a connection section positioned between the evaporation section and condensation section. The evaporation section and condensation section are respectively arranged in the chamber on two sides thereof. The connection section has a set of first communication holes and a set of second communication holes in communication with the evaporation section and condensation section. The evaporation section and condensation section respectively have multiple first and second flow guide bodies, which are arranged at intervals to define therebetween first and second flow ways. Each of the first and second flow ways has a narrower end and a wider end. The first flow ways communicate with a free area. The condensation section is designed with a low-pressure end to create a pressure gradient for driving a working fluid to circulate without any capillary structure.