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Gravitational lensing,light from the background sources bended by foreground massive objects predicted by the General Relativity,has been adopted as an efficient tool to study the mass distribution in the universe.Ringsin the present paper are the results of galaxy-galaxy strong lensing,which have been found widely in individual surveys. It can be estimated theoretically that there should be about 10 gravitational rings observed per square degree in the current surveys.While isolatedringsappearing in the field are relatively easy to study,they can be considered to constrain the slope of the density profiles of clusters if they appear in the cluster environment since the conditions ofringsformation are sensitive to the external shear and convergence produced by nearby mass condensations. In the present paper,the current observational projects and the relative studies onringsare briefly introduced for both SLACS(Sloan Lens ACS) survey and SL2S(Strong lensing legacy surveay) in CFHTLS(Canada-France-Hawaii Telescope Legacy Survey).The current conclusions from SLACS are as follows.(i) The slope of density profiles of the massive elliptical galaxies producedringsseems to be in consistence with the isothermal profile(with p∝r~(-2±0.13));(ii) The distributions of both position angles and ellipticities of baryonic matter trace their host dark matter halo well(with position angle difference between light and total mass〈△θ〉= 0°±3°degrees and ellipiticity ratio〈q_(SIE)/q_*〉= 0.99). The studies ofringsoccur in cluster environment are also summarized including simulations and the applications ofringsto constrain the slope of mass profile of a clusters,and the conclusions are positive.Comparing to theringsin field,theringsin cluster environments show some special features.(i) As galaxies are crossing the higher density region of the cluster,the DM halo component is tidally stripped.(ii) The ring cross-section is considerably increased near critical lines.(iii) The geometry of theringsin cluster is different from that of theringsin field.Since the SL2S is providing a large sub-sample of gravitational rings around massive distant elliptical galaxies in the outskirts of galaxy clusters.The systematic study of gravitational rings around cluster members can provide new tests on the ACDM cosmology at galaxy scales.