Abstract: The label positioning detector in GDX6S packer was not able to identify a packet which was not squarely wrapped, therefore the detector was improved. A reflective optical fiber sensor was fixed on the arc plate of wheel No. 3, which could detect protrusive part of a label, and the packet wrapped in an obliquely folded label would be automatically rejected at the rejecting outlet of wheel No. 3 by a control system. The results of application showed that:the improved detector ran stably and reliably, it automatically detected and rejected the packet which was not squarely wrapped, the rejection rate increased from 27.9% to over 95.4%. It took 0.5 min for treating a fault on an average contrasting with 3 min before, the package quality and the efficiency of equipment were improved.