The invention provides a nanosecond level time precision measuring method and device for network signal transmission time delay. Two time recorders (101) are arranged to receive arrival time of Ethernet frame signals in the sending and receiving ends of the network respectively, transmission time delay of the network signal is obtained by subtracting the arrival time in the sending end from that of the receiving end, each time recorder comprises a GNSS receiver (102), a frame head detection module (103), a time calibration module (104) and a time recording module (105), the frame head detection module (103) receives a frame head detection result to the time recording module (105) when receiving the Ethernet frame signal, the GNSS receiver (102) provides accurate time information, the timecalibration module (104) calibrates local time via the accurate time information provided by the GNSS receiver (102), and the time recording module (105) records the calibrated present time by takingoutput of the frame head detection module as a triggering signal.