A method for audio-video synchronization in a virtual reality system, wherein the VR system comprises a VR device (12, 52, 72) and a host device (11, 51, 71), the method comprising: connecting the VR device (12, 52, 72) to a host device (11, 51, 71) via a data transmission interface; transmitting an audio signal and a video signal from the host device (11, 51, 71) to the VR device (12, 52, 72); estimating time delay information in an audio transmission path and a video transmission path of the VR device (12, 52, 72); transmitting a feedback signal recording the time delay information from the VR device (12, 52, 72) to the host device (11, 51, 71); adjusting timing of the audio signal or the video signal transmitted from the host device (11, 51, 71) to the VR device (12, 52, 72) according to the feedback signal; determining a first delay of the audio signal and a second delay of the video signal in the audio transmission path and the video transmission path in the VR device (12, 52, 72), respectively; determining whether the first delay or the second delay is longer than a first threshold; determining whether the first delay or the second delay is longer than a second threshold when it is determined that the first delay or the second delay is longer than the first threshold; when it is determined that both the first delay and the second delay are not longer than the second threshold, adjusting timing of the audio signal or the video signal transmitted from the host device (11, 51, 71) to the VR device (12, 52, 72) according to the feedback signal; and when it is determined that the first delay or the second delay is longer than the second threshold, re-transmitting the audio signal and the video signal from the host device (11, 51, 71) to the VR device (12, 52, 72). connecting the VR device (12, 52, 72) to a host device (11, 51, 71) via a data transmission interface; transmitting an audio signal and a video signal from the host device (11, 51, 71) to the VR device (12, 52, 72); estimating time delay information in an audio transmission path and a video transmission path of the VR device (12, 52, 72); transmitting a feedback signal recording the time delay information from the VR device (12, 52, 72) to the host device (11, 51, 71); adjusting timing of the audio signal or the video signal transmitted from the host device (11, 51, 71) to the VR device (12, 52, 72) according to the feedback signal; determining a first delay of the audio signal and a second delay of the video signal in the audio transmission path and the video transmission path in the VR device (12, 52, 72), respectively; determining whether the first delay or the second delay is longer than a first threshold; determining whether the first delay or the second delay is longer than a second threshold when it is determined that the first delay or the second delay is longer than the first threshold; when it is determined that both the first delay and the second delay are not longer than the second threshold, adjusting timing of the audio signal or the video signal transmitted from the host device (11, 51, 71) to the VR device (12, 52, 72) according to the feedback signal; and when it is determined that the first delay or the second delay is longer than the second threshold, re-transmitting the audio signal and the video signal from the host device (11, 51, 71) to the VR device (12, 52, 72).