A method for synchronously implementing media switch in gateways used for IP FAX is disclosed. The method comprises sending a message for notification of fax event from a media gateway which firstly detects a fax event to the other media gateway of the fax event; implementing a media switch in the media gateway which firstly detects the fax event into fax mode; implementing a media switch in the other media gateway of the fax event into fax mode after receiving said message for notification of fax event. Therefore, the method of the invention overcomes the disadvantages of the related art and more particularly prevents fax failure due to difference of routing for a born network and cross-domain. The IP FAX used by the method of the invention can be applied broadly as the method also improves compatibility and reliability for IP FAX.