In the construction of a deep-water embedded cap foundation，it was required to excavate the mud surface to the depth below sealing concrete and clean the bottom carefully，ensuring the height and quality of bottoming concrete.For hard rock under good geological conditions，there exist such problems as difficulty in excavation，long excavation time consumption，and high construction cost.Based on the construction of the main pier caps of the Chongqing Jiahua Metro Bridge，this paper adopted the method of combining theoretical analysis，numerical calculation，and engineering implementation verification，which developed an emended cap unsealed bottom key construction techniques for deep-water hard rock.This construction technology used the method of excavating the wall foundation groove and pouring the foundation groove concrete to replace the large volume of bottom-sealing concrete as a way to achieve the purpose of providing a dry working environment for the construction of the cap.With this method，shorter underwater excavation time，reduced underwater concrete amount，improved construction efficiency，lowered construction time and are achieved.