Based on the concepts of “role identity”, “group identity” and “person identity” in social psychology, this paper tries to find out the role identities of the co-translators and the group identities aggregated from different roles. It is found that the Chinese and foreign scientific and technological co-translators in the Ming and Qing dynasties were mainly foreign missionaries and local literati intellectuals, and the main sponsors were the missionary societies and government agencies. It is further found that scientific and technological co-translation in the Ming and Qing dynasties showed a tendency from being driven by private interactions to being driven by specific goals, from the passive participation of translators to their active initiation, and from the folk workshop mode to the government- sponsored mode. The sorting out of the identities of these scientific and technological co-translators helps to present the nature of Sino-foreign co-translation in the two dynasties, and to pave the way for further studies on the co- translation groups and the behavior of co-translators.