A low speed encoding method based on Internet protocol (IP) includes the steps of determining speech characteristic parameters in TN duration, determining an optimized frame length T for successive speech data processing according to the characteristic parameters, making compressed encoding of the speech data in every T, assembling a packet of the encoded bits with TCP and UDP, again assembling a packet of the assembled bits with IP, and finally outputting the channel. The method uses a single frame, variable length frame, intra-frame adaptive low speed speech encoding method, which has the advantages of reducing the bit rate and raising transmission efficiency. The method takes an optimized length encoded frame as a unit to break the IP datagram, and therefore raises encoding and decoding quality of the speech data greatly. Informal tests show that the method can raise a MOS (mean opinion score) value from 0.1 to 0.2.