Now for orthodontists there are no commercial orthodontic EMR systems suitable for their clinical needs in China, so we study orthodontist’s daily workflow, analyze the requirements, and finally develop the orthodontic EMR Cloud for Peking University School of Stomatology. We propose and adopt 2-Tier Cloud-ARchitecture (2TCAR), which contains rich client tier based on Rich Internet Application (RIA) and server-side Cloud tier based on SimpleDB, to develop the orthodontist’s EMR Cloud for orthodontics according to orthodontist’s workflow. In the 2TCAR the rich client tier is maximized to implement almost all functionalities of user interfaces and transaction logic in the EMR. Functionalities in server-side Cloud tier are simplified only to implement data storage and query. Communication between the two Cloud tiers is also simplified via REST. In the article we research corresponding technologies such as Cloud computing, REST, Flex in RIA and SimpleDB Cloud. Further, in the orthodontic EMR Cloud we use Flex to implement UI presentation & interaction, transaction logic, and REST requests & responses in rich client tier; then design SimpleDB Cloud in server-side Cloud tier, and communication between two tiers via REST. And the EMR Cloud is integrated with existing Resister, Ward and Drugstore information systems. The practice shows that the orthodontic EMR Cloud based on the 2TCAR can fit seamlessly into orthodontist’s daily workflow and effectively replace current paper medical records.