In optical communication system，high-order modulation technology can realize higher system capacity and higher spectral efficiency with lower rate，PAM4 format provides an effective solution for high-speed Ethernet. A PAM4 transmission scheme is described，andan experimentalscheme forthe transmission of 5 Gbit/s PAM4signalis realizedby usingthedual-channelcouplingmethodofcommercial2.5GHzopticalcomponents.Anoff-lineDSPschemeisdesigned to optimize the data of experimental results. The experiment results show good eye diagrams，which indicates that the proposedschemecanimprovethetransmissionefficiencyofthesystemwhenappliedtoshortdistanceinterconnection.