The invention relates to the technical field of exploration parts, in particular to a combined type drill stem which comprises an outer sleeve rod and an inner lining rod inserted in the outer sleeverod. The outer surface of the inner lining rod is provided with a plurality of spline edges. Every two adjacent spline edges and the inner wall of the outer sleeve rod form a medium channel, and one medium channel is an oil injection channel. The two ends of the outer sleeve rod are fixedly provided with a male connector and a female connector respectively. A first annular groove is formed in theouter wall surface of the outer end of each male connector and internally provided with an expansion oil bag. A load-bearing cylinder is arranged at the rear end of each female connector. A weight-reducing chamber is formed in the front end of each load-bearing cylinder. An oil injection groove communicated with the interior of the corresponding expansion oil bag is formed in each male connector and communicated with the oil injection channel. The two end faces of the inner lining rod are provided with a rotating ring and a sealing ring respectively. The connection stability between two adjacent drill stems can be enhanced, and the frequent drill stem lifting actions can be satisfied.