The invention relates to an extension-type tension leg platform comprising a rectangular circular float box unit composed of four float boxes. A column floating on water is fixedly connected to the upper surface of each of four intersections of the float box unit. The extension-type tension leg platform is characterized in that the horizontal center line of each column and the horizontal center line of the float box unit form an included angle alpha; every column extends out of the float box unit; the outside of the tail end of each column extending out is provided with a plurality of tension leg suspension points; a tension leg is suspended to each tension leg suspension point; the tail end of every tension leg is fixedly connected to seabed mud; a deck mainly used for holding oil production equipment, oil-gas treatment equipment and drilling and workover equipment is fixedly connected to the top ends of the columns. The extension-type tension leg platform has the advantages that the platform has high resistance to severe weathers, stability is high, installation risk is low, and installation cost is low.