The invention discloses a frame structure applicable to giant karst cave protection and a construction method thereof. The frame structure comprises a plurality of frame columns, main beams, secondarybeams and a protecting net and is characterized in that each frame column comprises a plurality of I type steel pipes and II type steel pipes which are sequentially connected together in an alternating manner; the I type steel pipes are frame column connector sections, and the II type steel pipes are frame column extension sections; each I type steel pipe is provided with connectors; the main beams are horizontally arranged, two ends of the main beams are connected with the connectors of adjacent frame columns to integrally connect the frame columns, and the main beams located on the top layer are connected through the secondary beams; the protecting net is arranged in a space formed by the secondary beams and the main beams. The frame structure spliced by split standard parts is fast informing, high in safety and stability, convenient to demount, capable of effectively guaranteeing the safety of high-altitude operators and significant to construction safety guaranteeing in a giant karst cave.