Aluminum drill pipe has the advantages of low density, high specific strength and strong corrosion resistance, but the wear resistance is low. In the practical application, the aluminum drill pipe body and steel tool joints are assembled together to form a drill string, the steel tool joints are used to withstand the screwing and unloading operation. Because of the differences of aluminum and steel in the elastic modulus, thermal expansion coefficient and the yield strength, the unreliable connections often happen. The theoretical calculations of interference are made on aluminum drill pipe with internal upset, which has the diameter of 147mm and wall thickness of 13mm, the interference range should be 0.712～1.009mm to meet transfer load without plastic deformation. The paper also introduces the assembly process of drill rod and steel joint.