The invention discloses a thermal assembly device used for connecting an aluminium alloy drill rod body with a steel joint. The thermal assembly device comprises a steel joint heating mechanism, a feeding mechanism, a steel joint rotation mechanism, a rod body clamping mechanism, an internal aluminium alloy drill rod body cooling mechanism, an external steel joint cooling mechanism, a parameter detection mechanism and an experiment bench. The thermal assembly device is adopted to assemble the aluminium alloy drill rod body and the steel joint. In thermal assembly, at first, the steel joint is heated to a certain temperature to be expanded, then screwed on the aluminium alloy drill rod body in the thermal state, and next cooled, and a certain pretightening force can be obtained at the threaded connection after cooling, so that the requirements of torque transmission and load bearing of the aluminium alloy drill rod are met. The thermal assembly device can be used on the same experiment bench, the thermal assembly is realized only through replacing different materials and sizes of drill rod bodies and joints, and the connection strength and the connection reliability of the drill rod body and the steel joint are improved.