A time synchronization method is provided. Firstly, an update time of a second playing device is calculated according to a first system time of transmitting a first packet from a first playing device and a second system time of receiving the first packet by the second playing device. Then, a first difference value is calculated according to the first system time of transmitting a second packet from the first playing device and the update time corresponding to the reception of the second packet by the second playing device. If plural first difference values are all smaller than a first predetermined value, a second difference value is calculated. If the second difference value is smaller than a second predetermined value, a synchronization time is obtained according to the second difference value and the update time.