Abstract: In this paper, the line fault in the local area network of Neijiang Normal School's student dormitory is researched.The conclusion is obtained that the majority of network line faults are due to the bad line contact.On account of 4 lines idle in the network cable, a new idea is put forward that the correspondence information could be transferred again through the 4 idle lines.As a result, a new design for NIC is introduced, and the principle of its work is presented as well.