The 3R (re-amplification,re-shaping,re-timing) regeneration is one of t he key technologies for the high-speed optical communication systems.How to set the 3R regeneratio n system in the transmission line more reasonably and more efficiently might need to be solved i n the high-speed system.There is a regenerative capacity for any regeneration system,and the rege nerative capacity varies with input signals.So for the signal with a spec ific deterioration,testing the regenration effect cannot describe the regeneration capacity of the 3R syste m.Changing the deterioraton of the input signal,we can get the regenerative capacity of the 3R regeneration system,which is decided by the minimum input Q value and the maximum input Q value,an d the maximum regenerative capacity.In this paper,the regenerative curve for a 40Gbit/s 3R regeneration system is shown,which is based on four-wave mix ing in a dispersion shifted fiber (DSF). This all-optical 3R regeneration system can regenerate the degraded signals wit h a Q value ranging from 2.6to 5.8.The maximum improvem ent of the signal to noise ratio (SNR) is 1.1when the i nput SNR is 3.2.