The drive branches only subjected to axial loads, while the external loads beyond the end-constrained space are collectively borne by multiple constraint branches. This type of 2R1T parallel mechanisms (PMs), compared to traditional counterparts, exhibit superior force and load-bearing performance, particularly in eccentric heavy-load conditions. This paper introduces a novel type of 2R1T PMs with completely separated drive and constraint branches, along with its type synthesis method. A kinematic and static analysis is conducted on the typical 3UPS-3SS PM, and a comparison is made between the force performance of the 3UPS-3SS PM and traditional 3RPS PM under eccentric heavy -load conditions. These mechanisms hold extensive application prospects in situations requiring pose adjustment under eccentric heavy-load force conditions.