The utility model discloses a bottom connecting structure for a free standing hybrid riser. The bottom connecting structure comprises a main frame and a process pipeline. The main frame comprises four stand columns, wherein the stand columns are vertically arranged in parallel, the top ends of the four stand columns are connected end to end through horizontal supports I, and the bottom ends of the four stand columns are connected end to end through horizontal supports I; a supporting steel plate I is arranged on the upper surface of the main frame, and a supporting steel plate II is arranged on the lower surface of the main frame; a flange plate I is arranged on the supporting steel plate I, the supporting steel plate II is connected with a plug and socket connector, and the plug and socket connector extends downwards; every two adjacent stand columns are connected with inclined struts and transverse beams I, the free end of each inclined strut is connected with the free end of the corresponding transverse beam I, and the connection point between the free end of each inclined strut and the free end of the corresponding transverse beam I is further connected with a horizontal support II; a supporting steel plate III is arranged on a surface formed by the transverse beams I and the horizontal support II, and a flange plate II is arranged on the supporting steel plate III; one side of the main frame is connected with a counterweight, and the counterweight is arranged opposite to the inclined struts. The bottom connecting structure for the free standing hybrid riser has the following advantages that the drag area is small, the structure is simple, the weight is light, and the eccentricity is eliminated.