The Ca²⁺-ATPase of sarcoplasmic reticulum is a Ca²⁺ pump that plays a key role in regulating cytosol calcium concentration in muscle cells. It undergoes a sequential conformational transition during the transport process. According to the classical E1/E2 theory, in the E1 state the binding sites have high affinity and open to the cytoplasm, whereas in the E2 state the binding sites have low affinity and face the luminal side. Crystal structures of several states during the reaction cycle of Ca²⁺-ATPase have been solved recently, including a Ca²⁺-bound form (E1-2Ca²⁺), a Ca²⁺-unbound form stabilized by a potent inhibitor thapsigargin (TG) (E2-TG), an ATP-bound form (E1-ATP), an E1-P-ADP state, and an E2-Pi state. The details of these crystal structures and the relationship between structure and function of Ca²⁺-ATPase during reaction cycle were summarized, and the issues to be addressed in future research were raised.