Abstract: A bitemporal relational algebra based on the bitemporal conceptual data model （BCDM）, which is an important model in the temporal database. Firstly, the transaction time and valid time in database as well as the bitemporal element are defined formally, and then the bitemporal element calculus is described; secondly, temporal mapping is defined, which is used to describe the bitemporal relational tuple on BCDM, and then the temporal mapping calculus is described; Finally, bitemporal relation is defined as the set of the temporal mapping tuple, and the bitemporal relational algebra operations are described formally.