Tension control method of roller box type compact rolling mill for producing rod iron of large diameter

The invention relates to a tension control method in the metallurgical field, in particular to a rolling mill tension control method for producing a major-diameter coil rod by using a roll box-shaped compact type rolling mill. The control method comprises the following steps: adjusting rolling tension of rough and middle rolling mill units to the optimal state; recording a rolling current I1 of the rolling mill when a rolled piece passes through a No. 9 rolling mill and a No. 11 rolling mill of the middle rolling mill unit; recording a rolling current I2 of the No. 9 rolling mill or the No. 11 rolling mill again when the rolled piece is gripped into a No. 16 rolling mill of a CCR unit; comparing the rolling current I1 with the rolling current I2; improving the rotational speed of the No. 9 rolling mill or the No. 11 rolling mill to balance the tension when the rolling current I2 is less than the rolling current I1; and adjusting the telescoping amount of a loop according to the load current of the CCR unit af