Nowadays steel and concrete composite beams are widely applied in structures mainly subjected to dynamic loads, such as railway and road bridges exposed to traffic loads and industrial crane runways exposed to folk-lift truck loads, the fatigue resistance of these structures must be generally and carefully verified. And normally the shear forces between concrete flange and steel beams are all transferred by different kinds of shear connectors, fatigue failure of composite beam may happen on shear connectors. So the fatigue resistance of shear connectors in composite beams is significant for the safe of whole structure and needed to be well investigated. The fatigue strength of shear connectors could be explained in three ways, the fatigue endurance described by the relationships between stress range (S) and number of cycles (N), the static residual strength after a certain number of cycling loading, and the slip behavior during the cycling tests. S-N curves which widely used for steel fatigue assessment are also useful for shear connectors. Although there are already S-N curves for headed steel studs in Eurocodes and AASHTO, they are normally available for common studs. Whether these S-N curves applicable for large diameter studs or studs embedded in high strength concrete or other kind shear connectors is questionable. And the factors influencing fatigue life of shear connectors are needed more research. Furthermore, for the fatigue life assessment of existing structures, it is important to attain the residual strength after a certain service life or the principles of slip developing behavior during the service life. Then it is possible to assess how long the shear connectors could still service.