A method for processing non-standard facilities frames by T.38 gateways, wherein the T.38 gateways includes at least one transmitting gateway and at least one receiving gateway, the transmitting gateway is connected with a transmitting facsimile machine, and the receiving gateway is connected with a receiving facsimile machine. The method includes: a) the transmitting gateway and the receiving gateway determining the types of all received V.21 frames; b) when the receiving gateway or the transmitting gateway receives a non-standard frame NSF, modifying the non-standard frame NSF, so that the corresponding receiving facsimile machine or transmitting facsimile machine is unable to receive a correct NSF frame; c) the receiving gateway encapsulating the modified NSF frame data, or the transmitting gateway modulating the modified NSF frame data and transmitting the modulated frame data. The method modifies the rate negotiation performed with proprietary frames as a negotiation performed with standard frames.