The invention relates to a control method of a multi-cavity steel component assembling and positioning mechanism, and belongs to the technical field of multi-cavity steel component assembling equipment. The mechanism comprises a square tube positioning and pressing frame. Two ends of the square tube positioning and pressing frame are provided with square tube positioning and pressing pieces connected with the square tube positioning and pressing frame in a displacement mode. An electromagnet is arranged at a front end of an end primary positioning piece. A lower end of the end primary positioning piece is provided with an end primary positioning piece guide rail which is in sliding connection with the end primary positioning piece. A driving motor is arranged at the rear end of the end primary positioning piece. A rack guide rail parallel to the end primary positioning piece guide rail is arranged below the driving motor. The rack guide rail is movably engaged with the drive motor. Thelower end of a displacement cylinder is provided with a lock pressing piece which is movably contacted. Two ends of a pressing roller are provided with bearing seats which are movably sleeved with the pressing roller. Pressing cylinders are arranged on the bearing seats. According to the control method of the multi-cavity steel component assembling and positioning mechanism, the method has the advantages of being compact in structure, accurate in positioning and integrated in assembling and welding; and the machining precision of the multi-cavity steel components is improved, and the machining period is shortened.