THe present invention provides a control method of core rod time-delayed extension in the uncoiling process of hot coil box, mainly consists of coder for detecting angle, hydraulic rotary cylinder controlled by PLC proportion valve, transferring arm driven by hydraulic rotary cylinder and core rod which is positioned on the top end of transferring arm and can be extended. Said invention utilizes the mathematical model of residual weight of workpiece in the uncoiling process to make calculation and judgement. When the residual weight is greater than or equal to threshold value, it can be back retuned and continuously calculated, and when the residual weight is less than threshold value, the computer can give out instruction to make the core rod valve coil in the hot coil box be powdered on, the core rod can be extended out and inserted into the hot coil box.