Low-field NMR was used to study the effects of retarder HN-1 on the transverse relaxation time (T_2) and the states evolution of water in the cement paste. Analyses the results can be seen that the retarder HN-1 reduces the early hydration rate and extend the induction period of cement hydrated. The changes in the pore structure of hydrating cement paste are accompanied by changes of the states of water in cement paste such. Low-field NMR techniques can be used to observe these changes in the case without destroying the structure of the samples. It can be found from the changes of the relaxation time of water in the hardened paste that the relaxation time of volatile water in hardened paste tends to be shorter while curing time increases, and the migrated rate slows down with the increase of water-cement ratio and the amount of retarder, Capillary water gradually transforms into gel water and physically bound water. The decrease of the average relaxation time of main peak indicates the refining of pore structure in hardened paste. ?The study of X diffraction showed the addition of retarder only changed the process of hydration, but had no effect on the final hydration degree of cement paste.