It has been proposed to deploy relay nodes for the sake of prolonging Wireless sensor networks(WSN)lifetime, such that sensors transmit the sensed data to them which in turn delivers the data to base stations. For survivability requirements, relay placements which considers fault tolerant ability have been noticed and studied. While related works are limited or most existing works don’t take factors such as fault tolerance, or base stations into account comprehensively in two tired WSN. We focus on fault tolerant relay node placement in two-tiered heterogeneous WSN with base stations. As far as we know,fault tolerance contains two fundamental aspects, for one is multi-coverage and the second is multi-path. It is a NPhard problem and figure out an approximation, whose approximation ratio is enhanced to be(18 +). While a sub-problem approximation is also described as supplementary. Experimental results verify that the number of relay nodes deployed by our algorithm is somewhat superior to existed relay node placement solutions. It has been proposed to deploy relay nodes for the sake of such prolonging Wireless sensor networks (WSN) lifetime, such that sensors transmit the sensed data to them which turn to deliver the data to base stations. While related works are limited or most existing works do not take factors such as fault tolerance, or base stations into account comprehensively in two tired WSN. We focus on fault tolerant relay node placement in two-tiered heterogeneous WSN with base stations. As far as we know, fault tolerance contains two fundamental aspects, for one is multi-coverage and the second is multi-path. It is a NPhard problem and figure out an approximation, whose approximation ratio is enhanced to be (18+). While a sub-problem approximation is also described as supplementary. Experimental results that the number of relay nodes deployed by our algorithm is somewhat superior t orized relay node placement solutions.