With the demand for higher bandwidth applications increasing,internet is growing at incredible rate.Future all-optical networks are likely to be a hybrid of wavelength division multiplexing（WDM）and optical time division multiplexing（OTDM）networks by combining the advantages of both technologies.All-optical RZ to NRZ code conversion,which can reduce any optical-electrical-optical conversion and enable of data with different format transmission in the optical domain through different region of network freely,is one of the key techniques of constructing this network.The research progress of all-optical RZ to NRZ format conversion is introduced.And the operation principle,characteristics,advantages and disadvantages of these methods are analyzed.Also the current difficulties of the techniques are listed.Finally,the future development is prospected.