The invention relates to a two-segment type rotary excavating bottom-expanding drill bit. The drill bit is provided with a drilling bucket body used for installing expanding tool bits, the drilling bucket body is of a hollow cylinder structure, a center pole is arranged in the middle of the drilling bucket body, and the upper portion expanding tool bit and the lower portion expanding tool bit are installed inside the upper portion and the lower portion of the hollow cylinder of the drilling bucket body respectively, and used for two-segment bottom expanding, the upper portion expanding tool bit is connected with the center pole through a telescopic mechanism, the lower portion expanding tool bit is connected with the center pole through a telescopic mechanism, and therefore outward expanding or inward contracting of the tool bits is achieved. Through arranging the upper portion expanding tool bit and the lower portion expanding tool bit, the upper portion and the lower portion of an expanding head are formed in sequence, and in this way, stress of blade structure and needed power in the bottom expanding process are greatly reduced; small construction equipment can be adopted, in this way, construction efficiency is higher, larger-diameter bottom expanding can be achieved, the maximum bottom-expanding diameter is 2.2 times the diameter of the uniform cross section and can reach 4.7 m, and the bottom-expanding area is 4.9 times the area of the uniform cross section. The two-segment type rotary excavating bottom-expanding drill bit is reasonable in structural stress, small in load and high in using reliability and obviously lowers the construction cost.