The invention discloses a method for detecting network port performance of an IPTV set-top box. The device comprises the IPTV set-top box and a loop-back network cable, wherein the head end of the loop-back network cable is plugged into a network port of the IPTV set-top box (STB), so the IPTV set-top box is used for transmitting and receiving data packets through the loop-back network cable connected to the network port, and determining whether the loop-back network cable is connected correctly according to the transmitted data packets and the received data packets; and if the loop-back network cable is connected correctly, every performance index of the network port is detected in the processes of transmitting and receiving the data packets, every detected performance index is compared with a preset performance index threshold value, and the network port performance is determined whether to meet requirements or not according to a comparison result. By using the method and the device disclosed by the invention and inserting the loop-back network cable into the set-top box after the set-top box is started, the detection of every type of the performance indexes of the network port of the set-top box can be performed automatically.